The present invention relates to a method and apparatus in which a terminal performs contention-based access in a mobile communication system, wherein the method comprises: a sensing step of sensing whether or not contention-based access is allowed for at least one logical channel; a receiving step of receiving a contention-based reverse grant from a base station; and a transmitting step of transmitting data to the base station through the logical channel for which the contention-based access is allowed. According to the present invention, contention-based access can be efficiently performed, and the reliability of transmission can be ensured.