A receiving system and a data processing method for receiving and processing mobile service data are disclosed. The receiving system comprises a demodulating unit, a block decoder, a controller, and an RS frame decoder. The demodulating unit receives a broadcast signal including mobile service data and main service data and converts the received broadcast signal to a baseband broadcast signal. The mobile service data configure at least one of a primary RS frame and a secondary RS frame. The block decoder performs turbo decoding of a SCCC block unit for mobile service data within the baseband broadcast signal based on SCCC-related information. The controller generates a control signal for RS frame decoding with reference to at least one of SCCC block mode information, RS frame mode information, and user's input. The RS frame decoder configures at least one of a primary RS frame and a secondary RS frame using the mobile service data output from the block decoder in accordance with the control signal and performs error correction decoding for corresponding RS frame with reference to reliability information of each mobile service data byte within the configured RS frame.