diff --git a/src/core/diags/README.md b/src/core/diags/README.md
index 2ddb658ac..ee447b3f9 100644
--- a/src/core/diags/README.md
+++ b/src/core/diags/README.md
@@ -77,6 +77,15 @@ Stop transmitting continuous carrier wave.
 Done
 ```
 
+### diag frame \<frame\>
+
+Set the frame (hex encoded) to be used by `diag send` and `diag repeat`. The frame may be overwritten by `diag send` and `diag repeat`.
+
+```bash
+> diag frame 11223344
+Done
+```
+
 ### diag stream start
 
 Start transmitting a stream of characters.
@@ -143,11 +152,11 @@ RawPowerSetting: 223344
 Done
 ```
 
-### diag send \<packets\> \<length\>
+### diag send \<packets\> [length]
 
-Transmit a fixed number of packets with fixed length.
+Transmit a fixed number of packets.
 
-Length parameter has to be in range [3, 127].
+Send the frame set by `diag frame` if length is omitted. Otherwise overwrite the frame set by `diag frame` and send a frame of the given length(MUST be in range [3, 127]).
 
 ```bash
 > diag send 20 100
@@ -155,11 +164,11 @@ sending 0x14 packet(s), length 0x64
 status 0x00
 ```
 
-### diag repeat \<delay\> \<length\>
+### diag repeat \<delay\> [length]
 
 Transmit packets repeatedly with a fixed interval.
 
-Length parameter has to be in range [3, 127].
+Send the frame set by `diag frame` if length is omitted. Otherwise overwrite the frame set by `diag frame` and send a frame of the given length (MUST be in range [3, 127]).
 
 ```bash
 > diag repeat 100 100
diff --git a/src/core/diags/factory_diags.cpp b/src/core/diags/factory_diags.cpp
index 78845f1aa..03ce33d72 100644
--- a/src/core/diags/factory_diags.cpp
+++ b/src/core/diags/factory_diags.cpp
@@ -32,6 +32,7 @@
  */
 
 #include "factory_diags.hpp"
+#include "common/error.hpp"
 
 #if OPENTHREAD_CONFIG_DIAG_ENABLE
 
@@ -187,6 +188,7 @@ extern "C" void otPlatDiagAlarmFired(otInstance *aInstance) { otPlatDiagAlarmCal
 const struct Diags::Command Diags::sCommands[] = {
     {"channel", &Diags::ProcessChannel},
     {"cw", &Diags::ProcessContinuousWave},
+    {"frame", &Diags::ProcessFrame},
     {"gpio", &Diags::ProcessGpio},
     {"power", &Diags::ProcessPower},
     {"powersettings", &Diags::ProcessPowerSettings},
@@ -208,12 +210,31 @@ Diags::Diags(Instance &aInstance)
     , mChannel(20)
     , mTxPower(0)
     , mTxLen(0)
+    , mIsTxPacketSet(false)
     , mRepeatActive(false)
     , mDiagSendOn(false)
 {
     mStats.Clear();
 }
 
+Error Diags::ProcessFrame(uint8_t aArgsLength, char *aArgs[], char *aOutput, size_t aOutputMaxLen)
+{
+    Error    error = kErrorNone;
+    uint16_t size  = OT_RADIO_FRAME_MAX_SIZE;
+
+    VerifyOrExit(aArgsLength == 1, error = kErrorInvalidArgs);
+
+    SuccessOrExit(error = Utils::CmdLineParser::ParseAsHexString(aArgs[0], size, mTxPacket->mPsdu));
+    VerifyOrExit(size <= OT_RADIO_FRAME_MAX_SIZE, error = kErrorInvalidArgs);
+    VerifyOrExit(size >= OT_RADIO_FRAME_MIN_SIZE, error = kErrorInvalidArgs);
+    mTxPacket->mLength = size;
+    mIsTxPacketSet     = true;
+
+exit:
+    AppendErrorResult(error, aOutput, aOutputMaxLen);
+    return error;
+}
+
 Error Diags::ProcessChannel(uint8_t aArgsLength, char *aArgs[], char *aOutput, size_t aOutputMaxLen)
 {
     Error error = kErrorNone;
@@ -288,12 +309,25 @@ Error Diags::ProcessRepeat(uint8_t aArgsLength, char *aArgs[], char *aOutput, si
     {
         long value;
 
-        VerifyOrExit(aArgsLength == 2, error = kErrorInvalidArgs);
+        VerifyOrExit(aArgsLength >= 1, error = kErrorInvalidArgs);
 
         SuccessOrExit(error = ParseLong(aArgs[0], value));
         mTxPeriod = static_cast<uint32_t>(value);
 
-        SuccessOrExit(error = ParseLong(aArgs[1], value));
+        if (aArgsLength >= 2)
+        {
+            SuccessOrExit(error = ParseLong(aArgs[1], value));
+            mIsTxPacketSet = false;
+        }
+        else if (mIsTxPacketSet)
+        {
+            value = mTxPacket->mLength;
+        }
+        else
+        {
+            ExitNow(error = kErrorInvalidArgs);
+        }
+
         VerifyOrExit(value <= OT_RADIO_FRAME_MAX_SIZE, error = kErrorInvalidArgs);
         VerifyOrExit(value >= OT_RADIO_FRAME_MIN_SIZE, error = kErrorInvalidArgs);
         mTxLen = static_cast<uint8_t>(value);
@@ -316,12 +350,25 @@ Error Diags::ProcessSend(uint8_t aArgsLength, char *aArgs[], char *aOutput, size
     long  value;
 
     VerifyOrExit(otPlatDiagModeGet(), error = kErrorInvalidState);
-    VerifyOrExit(aArgsLength == 2, error = kErrorInvalidArgs);
+    VerifyOrExit(aArgsLength >= 1, error = kErrorInvalidArgs);
 
     SuccessOrExit(error = ParseLong(aArgs[0], value));
     mTxPackets = static_cast<uint32_t>(value);
 
-    SuccessOrExit(error = ParseLong(aArgs[1], value));
+    if (aArgsLength >= 2)
+    {
+        SuccessOrExit(ParseLong(aArgs[1], value));
+        mIsTxPacketSet = false;
+    }
+    else if (mIsTxPacketSet)
+    {
+        value = mTxPacket->mLength;
+    }
+    else
+    {
+        ExitNow(error = kErrorInvalidArgs);
+    }
+
     VerifyOrExit(value <= OT_RADIO_FRAME_MAX_SIZE, error = kErrorInvalidArgs);
     VerifyOrExit(value >= OT_RADIO_FRAME_MIN_SIZE, error = kErrorInvalidArgs);
     mTxLen = static_cast<uint8_t>(value);
@@ -420,12 +467,16 @@ exit:
 
 void Diags::TransmitPacket(void)
 {
-    mTxPacket->mLength  = mTxLen;
     mTxPacket->mChannel = mChannel;
 
-    for (uint8_t i = 0; i < mTxLen; i++)
+    if (!mIsTxPacketSet)
     {
-        mTxPacket->mPsdu[i] = i;
+        mTxPacket->mLength = mTxLen;
+
+        for (uint8_t i = 0; i < mTxLen; i++)
+        {
+            mTxPacket->mPsdu[i] = i;
+        }
     }
 
     mDiagSendOn = true;
@@ -986,4 +1037,5 @@ OT_TOOL_WEAK otError otPlatDiagRadioGetPowerSettings(otInstance *aInstance,
 
     return OT_ERROR_NOT_IMPLEMENTED;
 }
+
 #endif // OPENTHREAD_CONFIG_DIAG_ENABLE
diff --git a/src/core/diags/factory_diags.hpp b/src/core/diags/factory_diags.hpp
index 1b72a1563..cb1c7b95b 100644
--- a/src/core/diags/factory_diags.hpp
+++ b/src/core/diags/factory_diags.hpp
@@ -181,6 +181,7 @@ private:
 
     Error ParseCmd(char *aString, uint8_t &aArgsLength, char *aArgs[]);
     Error ProcessChannel(uint8_t aArgsLength, char *aArgs[], char *aOutput, size_t aOutputMaxLen);
+    Error ProcessFrame(uint8_t aArgsLength, char *aArgs[], char *aOutput, size_t aOutputMaxLen);
     Error ProcessContinuousWave(uint8_t aArgsLength, char *aArgs[], char *aOutput, size_t aOutputMaxLen);
     Error ProcessGpio(uint8_t aArgsLength, char *aArgs[], char *aOutput, size_t aOutputMaxLen);
     Error ProcessPower(uint8_t aArgsLength, char *aArgs[], char *aOutput, size_t aOutputMaxLen);
@@ -217,6 +218,7 @@ private:
     uint8_t       mChannel;
     int8_t        mTxPower;
     uint8_t       mTxLen;
+    bool          mIsTxPacketSet;
     bool          mRepeatActive;
     bool          mDiagSendOn;
 #endif
diff --git a/tests/scripts/expect/cli-diags.exp b/tests/scripts/expect/cli-diags.exp
index e5d2fbfab..b9ab58071 100755
--- a/tests/scripts/expect/cli-diags.exp
+++ b/tests/scripts/expect/cli-diags.exp
@@ -126,6 +126,35 @@ expect "start diagnostics mode"
 expect "status 0x00"
 expect_line "Done"
 
+send_user "input too short test\n"
+send "diag frame 11\n"
+expect "Error"
+
+send_user "input too long test\n"
+send "diag frame 11223344556677889900112233445566778899001122334455667788990011223344556677889900112233445566778899001122334455667788990011223344556677889900112233445566778899001122334455667788990011223344556677889900112233445566778899001122334455667788990011223344556677889900\n"
+expect "Error"
+
+send_user "input odd length test\n"
+send "diag frame 123\n"
+expect "Error"
+
+send_user "shortest frame test\n"
+send "diag frame 112233\n"
+expect "Done"
+send "diag send 1\n"
+expect "length 0x3"
+expect "Done"
+
+send_user "longest frame test\n"
+send "diag frame 11223344556677889900112233445566778899001122334455667788990011223344556677889900112233445566778899001122334455667788990011223344556677889900112233445566778899001122334455667788990011223344556677889900112233445566778899001122334455667788990011223344556677\n"
+expect "Done"
+send "diag repeat 1\n"
+expect "length 0x7f"
+expect "Done"
+
+send "diag repeat stop\n"
+expect "Done"
+
 send "diag channel 11\n"
 expect "set channel to 11"
 expect "status 0x00"