A method and apparatus are provided for controlling a data rate in a mobile communication system. The method includes changing an offset from a first offset used in a previous packet to a second offset determined based on whether or not the previous packet is successfully received by a second apparatus; determining whether or not a second channel quality in which the second offset is applied is within a range from a minimum quality to a maximum quality; if it is determined that the second channel quality is not within the range, determining that the offset is maintained as the first offset in a current packet; and transmitting, to the second apparatus, the current packet according to a first channel quality in which the first offset is applied.