A multiplexing method for multimedia communication is provided, which is compatible with the H.223 protocol by changing a header of a multiplex protocol data unit (MUX-PDU). The multiplexing method includes the steps of encoding media data, and multiplexing the media data encoded in the step (a) in units of a predetermined frame, and inserting a second flag having a predetermined length with an auto-correlation into the frame after a first flag representing the opening and closing of the frame. Therefore, the probability of detecting the MUX-PDU by a receiver is increased by adding a flag having a high auto-correlation to the H. 223 MUX-PDU frame, thereby increasing error-resiliency.