A method and apparatus for transmitting audio data is disclosed. In the method of sending audio data, audio data to be sent are divided into basic channel audio data and supplementary audio data for services of a high channel. When a left channel or a right channel is selected in response to a word selection signal in accordance with the standards of a serial bus, the basic channel audio data corresponding to a selected channel are sent, and at least one of the supplementary audio data is sent during the remaining time until another channel is selected in response to the word selection signal. Accordingly, audio data of a high channel, such as a 5.1 channel, can be sent without a design change using a serial bus for supporting a 2 channel, such as an I2S bus.