A digital broadcasting system and a data processing method are disclosed. The data processing method includes receiving a broadcast signal in which main service data and mobile service data are multiplexed, demodulating the broadcast signal to acquire fast-information-channel signaling information including reference time information for a system clock, and outputting demodulation time information of a specific position of a frame of the broadcast signal, decoding the fast-information-channel signaling information, and establishing the reference time information as the system clock at a demodulation time according to on the outputted demodulation time information and decoding the mobile service data according to the system clock.