AgInS 2 nanoparticles with superior visible light photocatalytic activity were successfully synthesized by a microwave hydrothermal method. This method is a highly efficient and rapid route that involves no organic solvents, catalysts, or surfactants. The photocatalytic activity of AgInS 2 nanoparticles was investigated through the degradation of dyes under visible light irradiation. Compared with TiO 2−x N x , AgInS 2 has exhibited a superior activity for photocatalytic degradation MO under the same condition. The experiment results showed that superoxide radicals (O 2 − ), hydrogen peroxides (H 2 O 2 ) and holes (h + ) were the mainly active species for the degradation of organic pollutants over AgInS 2 . Through the determination of flat band potential, the energy band structure of the sample was obtained. A possible mechanism for the degradation of organic pollutant over AgInS 2 was proposed.