A digital broadcasting system and a method of processing data are disclosed. Herein, additional encoding is performed on mobile service data, which are then transmitted, thereby providing robustness in the processed mobile service data, so that the mobile service data can respond more strongly against fast and frequent channel changes. In a transmitting system including a service multiplexer and a transmitter located in a remote site, a method of processing data of the transmitting system includes comparing an output data rate of the service multiplexer and a transmission data rate of the transmitter, when a difference occurs between the two data rates, adjusting a burst size, wherein the burst transmits mobile service data, and encoding the mobile service data, and referring to the burst size so as to multiplex main service data and the encoded mobile service data in a burst structure.