A method for synchronizing connection identifiers (CIDs) in a communication system includes sending a first message for requesting addition of a service flow identified by a CID; sending a second message and, at the same time, setting a number of a frame where the second message is transmitted as a first start frame number; sending a third message and, at the same time, setting a number of a frame where the third message is transmitted as a second start frame number; performing a modulo operation on a frame having the first or second start frame number and its succeeding frames using a positive integer for each frame, and detecting a number of a frame where a result value of the modulo operation becomes zero; and simultaneously updating CID lists at a frame having the detected frame number with regard to a CID of the added service flow.