A method for providing a buffer status report in a mobile communication network is implemented between a base station and a user equipment. When data arrives to buffers of the user equipment and the priority of a logical channel for the data is higher than those of other logical channels for existing data in the buffers, a short buffer status report associated with the buffer of a logical channel group corresponding to the arrival data is triggered. The user equipment is based on obtained resources allocated by the base station to fill all data of the buffer of the logical channel group in a Protocol Data Unit. If all data of the buffer of the logical channel group corresponding to the arrival data can be completely filled in the Protocol Data Unit, the short buffer status report is canceled. Otherwise, the user equipment transmits the short buffer status report.