A method and UE apparatus are provided for adjusting an uplink data rate by a User Equipment (UE) in a mobile communication system. The method includes determining if a current state of a buffer is an empty state or a non-empty state; when the current buffer state is the non-empty state, comparing a ratio of a total of transmission data currently stored in the buffer to a total of Transport Formats (TFs) allocated during a predetermined number n of subframes, with a predetermined threshold; setting indication information indicating satisfaction/non-satisfaction (‘happy bit(s)’) of an uplink data rate according to the comparison result; and transmitting the set indication information to a Node B. The UE apparatus comprises a multiplexing/demultiplexing device, a HARQ processor, a controller to set information indicating satisfaction/non-satisfaction in accordance with pre-set rules, an exemplary set of which is also provided.