The autocorrelation peak reduction due to wavelength mismatches between an encoder and a decoder in wavelength hopping-time spreading (WH-TS) two-dimensional optical CDMA systems is analyzed and verified by experiments. The tolerance of the wavelength mismatch is then obtained through the analysis of the system bit error rate (BER) performance. The results show that no significant BER performance is degraded only by the wavelength mismatches less than 0.1 nm which corresponds to 25 percent of the typical fiber Bragg gratings' spectral width.