A DTV transmitting system includes two pre-processors. The first pre-processor codes high-priority enhanced data for forward error correction (FEC) and expands the FEC-coded data. The second pre-processor codes low-priority enhanced data for FEC and expands the FEC-coded low-priority enhanced data. The DTV transmitting system further includes a data formatter generating enhanced data packets including the pre-processed data, a multiplexer multiplexing the enhanced data packets with main data packets, an RS encoder RS-coding the multiplexed data packets, a data interleaver interleaving the RS-coded data packets, and a block processor which codes each block of enhanced data in the interleaved enhanced data packets and bypasses the interleaved main data packets.