A receiving system and a method of processing broadcast signal. The receiving system includes a signal receiving unit, an equalizer, a block decoder, and an RS frame decoder. The signal receiving unit receives and demodulates a broadcast signal. The equalizer channel-equalizes a data group included in the demodulated broadcast signal. The block decoder performs turbo-decoding on mobile service data of the channel-equalized data group. And, the RS frame decoder determines a number of CRC errors of an RS frame including the turbo-decoded mobile service data, generates a reliability map including reliability information corresponding to each data byte of the RS frame. Herein, the reliability information is set-up as a soft value. Also, for each column, when the number of the determined CRC errors is greater than a number of RS parity bytes of the RS frame, the RS frame decoder sets a predetermined number of erasure points in the corresponding data bytes starting from the lowest reliability value for the corresponding column, and performs RS-erasure decoding on the column.