The disclosure relates to a method and apparatus for reporting a radio link failure (RLF) in a mobile communication system. According to an embodiment of the disclosure, a method, performed by a user equipment, of reporting an RLF includes detecting a first RLF during use of a first radio access technology (RAT), accessing a base station by using a second RAT different from the first RAT, and transmitting a report on the first RLF to the base station by using the second RAT.