A method of providing state information of a mobile station in a mobile communication system which provides a data service between the mobile station and a base station and transmits information on a maximum data rate available for the mobile station and information on the amount of data stored in a buffer of the mobile station in a reverse direction, such that the base station determines a reverse data rate of the mobile station based on channel state information transmitted in the reverse direction. The mobile station determines information on the amount of data stored in its buffer based on information transmitted from the base station. The mobile station quantizes the determined information on the amount of data stored in the buffer, and transmits the quantized information to the base station.