A digital broadcast system and a method of processing data are disclosed. The receiving system of the digital broadcast system includes a signal receiving unit, a first data processor, a second data processor, and an A/V decoder. The signal receiving unit receives at least one of first mobile service data that is transmitted according to a first transmission method and second mobile service data that is transmitted according to a second transmission method. The first data processor performs demodulation on the first mobile service data received by the signal receiving unit using a first demodulation method and corrects errors occurring in the demodulated first mobile service data. The second data processor performs demodulation on the second mobile service data received by the signal receiving unit using a second demodulation method and corrects errors occurring in the demodulated second mobile service data. The A/V decoder performs A/V decoding on mobile service data outputted from at least one of the first and second data processors.