A digital broadcasting system and method of processing data are disclosed. Herein, a transmitting system within the digital broadcasting system includes a byte-symbol converter, an interleaving unit, a block formatter, and a trellis encoding module. Herein, the byte-symbol converter converts inputted mobile service data to symbol units. The interleaving unit is provided with (N−1) number of block interleavers in parallel, and interleaves the symbols outputted from the byte-symbol converter. The block formatter controls output orders of the mobile service data being inputted and data being outputted from each block interleaver within the interleaving unit. The trellis encoding module is provided with a plurality of trellis encoders in parallel, and enables each trellis encoder trellis-encode the mobile service data.