Abstract: The feasibility to enhance the visible light-induced photocatalytic reduction efficiency of Cr(VI) in the presence of methyl orange (MO) and sulfate-modified titania-bearing blast furnace slag (STBBFS) photocatalyst was investigated at the different pH and different initial concentrations. The results showed that in the presence of MO, the photocatalytic reduction efficiency of Cr(VI) is significantly enhanced and the kinetic constant of compound systems is nearly 1.35 times higher than that of single Cr(VI). There exists a strong synergistic effect in the compound system, and the synergistic effect factors of Cr(IV) and MO are 18.3 and 39.8, respectively. During the whole experiment, the reduction efficiency of Cr(VI) and the decoloration efficiency of MO in the compound system are much higher than that of other two single systems. The presence of Na2SO4, NaCl, or NaNO3 in the reaction mixture has little effect on Cr(VI) reduction, but has a significant influence on the decoloration efficiency of MO.