A method and an apparatus for detecting a man-in-the-middle attack, where the method includes receiving, by a macro evolved Node B (MeNB), a first check request message sent by a secondary evolved Node B (SeNB), where the first check request message includes first identifier information and a first data packet count value, generating a second check request message according to the first identifier information, sending the second check request message to a user terminal, receiving a first check response message generated by the user terminal according to the second check request message, where the first check response message includes second identifier information and a second data packet count value, determining, by the MeNB, that the man-in-the-middle attack exists between the SeNB and the user terminal when the first data packet count value is different from the second data packet count value.