A comparative study of the photocatalytic performance for the degradation of rhodamine B (RhB) and methyl orange (MO) by ZnIn2S4 under visible light irradiation was investigated based on the adsorption of dyes, the active species generated during the photocatalytic process and the degradation pathway. The results show that 97.8% of RhB and 5.6% of MO were degraded under the same conditions, respectively. Photocatalytic degradation of RhB was obviously superior to degradation of MO. The adsorption of MO was almost negligible and 56.8% of RhB was adsorbed on ZnIn2S4. Superoxide radical was the key active species, and hydroxyl radical played a supplementary role during photocatalytic process. Different chemical bonds with different bond energies were destroyed when degradation of RhB and MO. Photocatalytic degradation of RhB was superior to that of MO because the excellent adsorptivity of RhB than that of MO, and the C&z.dbd; N bond of RhB was easier destroyed compared with azo bond of MO under the same conditions. The photocatalytic degradation of MO in a system in which superoxide radical was key active species can be improved by adding hole scavengers to inhibit recombination of holes and electrons, which would result in more electrons reducing oxygen to superoxide radical.