A method of inter-RAT failure event report is proposed. A UE detects a failure event in a first cell served by a first base station, and the first cell belongs to a first RAT. The failure event may include a radio link failure or a handover failure. The UE then performs an RRC establishment procedure with a second cell served by a second base station, and the second cell belongs to a second RAT. After the RRC establishment, the UE transmits a failure event report to the wireless network. The failure event can be a radio link failure, or be associated with a mobility command such as a handover command. By providing more reliable information in the failure event report than a network solution could provide, inter-RAT mobility performance can be improved.