A reverse data rate controlling method in a mobile communication system for transmission of packet data is provided. In an embodiment of the present invention, an RRL (Reverse Rate Limit) message includes an ignore RAB (Reverse Activity Bit) field to ensure a predetermined data rate for a particular access terminal (AT). In another embodiment of the present invention, an access probability is set for each data rate in the RRL message. Upon receipt of an RAB, an AT compares a random number with the access probability for its data rate and increases or decreases the data rate according to the comparison result.