A method of discarding logged measurements in a wireless communication system is provided. A user equipment in a Radio Resource Control (RRC) connected mode receives a Minimization of Drive Tests (MDT) configuration from a base station and starts a validity timer upon receiving the MDT configuration. The user equipment in an RRC idle mode logs measurements based on the MDT configuration to collect logged measurements while the validity timer is running. When the validity timer is expired, the user equipment discards the MDT configuration and starts a conservation timer. When the conservation timer is expired, the logged measurements are discarded.