A DTV transmitting system includes a first pre-processor for coding first enhanced data having a high priority for forward error correction (FEC) at a first coding rate and expanding the first enhanced data at a first expansion rate, and a second pre-processor for coding second enhanced data having a low priority for FEC at a second coding rate and expanding the second enhanced data at a second expansion rate. The receiving system further includes a data formatter for generating enhanced data packets, a multiplexer for multiplexing the enhanced data packets with main data packets, an RS encoder for RS-coding the multiplexed data packets, and a data interleaver for interleaving the RS-coded data packets and outputting a group of interleaved data packets having a head, a body, and a tail.