A digital television transmitting system includes a pre-processor, a packet generator, an RS encoder, and a trellis encoder. The pre-processor pre-processes enhanced data by coding the enhanced data for first forward error correction and expanding the FEC-coded enhanced data. The packet generator generates enhanced data packets including the pre-processed enhanced data and main data packets and multiplexes the enhanced and main data packets. Each enhanced data packet includes an adaptation field in which the pre-processed enhanced data are inserted. The RS encoder performs RS encoding on the multiplexed data packets for second forward error correction, and the trellis encoder performs trellis encoding on the RS-coded data packets.