A data slicer includes an error bit predictor, a DC level compensator, a co-channel detector, and an output device. The data slicer generates four bytes according to four slicing levels respectively. The four slicing levels are a DC level, a level generated by adding a predetermined offset to the DC level, a level generated by subtracting the predetermined offset from the DC level, and a compensated level generated by the DC level compensator. The co-channel detector determines if the compensated level has the co-channel interference. The output device generates an output byte according to indication signals generated by the co-channel detector and the error bit predictor and the parity check of the four bytes.