A method of processing broadcast data in a broadcast transmitting system includes randomizing mobile service data bytes; generating a Reed-Solomon (RS) frame; dividing the RS frame into RS frame portions; converting data bytes of the RS frame portions into data bits; encoding each converted data bit and outputting data symbols corresponding to the encoded data bits; interleaving the data symbols; converting the interleaved data symbols into data bytes; forming data groups including mobile service data corresponding to the converted data bytes, each of the data groups including known data sequences, signaling information, non-systematic RS parity data place holders and MPEG header data place holders; removing the non-systematic RS parity data place holders in the data groups and replacing the MPEG header data place holders in the data groups with MPEG header data to output mobile service data packets; and randomizing the MPEG header data in the mobile service data packets.