Disclosed is a method of setting an initial transport format combination (TFC) in a MAC layer of a CDMA system. the MAC layer selects the initial maximum useable TFC value using transport format set (TFS) and transport format combination set (TFCS) information received from a radio resource control (RRC) layer during an initialization of a channel setting among respective layers, and sets the initial maximum useable TFC by transmitting the initial maximum useable packet data unit (PDU) value to the respective radio link control (RLC) layers according to the selected initial maximum useable TFC value. The RLC layer sets the proper maximum PDU by comparing the initial maximum useable PDU value predetermined during the above process with buffer occupancy (BO), and if the initial data is generated, it transmits the data of a proper size to the MAC layer at the transmission time interval (TTI) when the initial data is generated.