An apparatus and method for a radio resource control (RRC) protocol to re-establish connection in a mobile communication system environment are disclosed. A user equipment (UE), for performing connection re-establishment in a connected state with connection to a mobile communication system is provided. When a network problem occurs, the UE shall proceed with the RRC protocol connection re-establishment procedure if the security has been activated. However, if the security has not been activated and the Radio Link Control (RLC) protocol indicates the maximum number of re-transmission has been reached, the UE shall reset lower layers of the RRC protocol, release unnecessary radio resources, and indicate the release of the RRC protocol connection to upper layers of the RRC protocol. Then the UE enters the idle state and waits for the next trigger event.