A buffer state reporting method of a terminal in a mobile communication system and a device are provided to transmit a report about a buffer state by including buffer state elements distinguished by a case before transmission resources are allocated and a case after the transmission resources are allocated, thereby efficiently reporting a buffer state. The first buffer state report is configured by including buffer state elements for at least more than one buffer having high priority among at least more than one of buffers for storing data according to at least one service(510). The first buffer state report is transmitted to a node B(507) through a shared channel(515). Transmission resources for considering the first buffer state report are allocated from the node B(507)(520). Uplink data and the second buffer state report including buffer state elements for the rest of the buffers except the at least more than one buffer having the high priority are transmitted to the node B(507) through the allocated transmission resources(525).