The present invention relates to a digital broadcasting system for transmitting/receiving a digital broadcasting signal and a method of processing data. In one aspect of the present invention provides a method of processing data, the method including receiving a broadcasting signal in which mobile service data and main service data are multiplexed, demodulating the received broadcasting signal, obtaining an identifier indicating that data frame of the broadcasting signal includes service guide information, decoding and storing the service guide information from the data frame; and outputting a service included in the mobile service data according to the decoded service guide information.