Radio link Failure (RLF) reporting operation in a wireless communication system using multiple cells is disclosed. According to this operation, when a first cell and a second cell are simultaneously connected to a UE and the first cell and the second cell are of different base stations (a first base station and a second base station respectively), if the RLF with the UE on the first cell is detected by the first base station, the first base station may transmits an indication of the RLF with the UE on the first cell to the second base station.