The invention proposes a method and an apparatus for transmitting a buffer status report in a wireless network, where a user equipment is configured with a plurality of component carriers, the user equipment obtains an amount of data to be transmitted after respective media access layer protocol data units corresponding to the respective component carriers are generated, generates the uplink buffer status report message according to the amount of data to be transmitted, and reports the uplink buffer status report message to a base station serving the user equipment. The invention address the problem of how to report buffer status information when there are a plurality of media access layer protocol data units in a transport time interval. With the solution of the invention, the base station can definitively know how many uplink resources can be allocated for the user equipment to guarantee more efficient scheduling.