The ternary solid solution BiOCl0.2Br0.1I0.7 was successfully synthesized using a wet chemical method. The visible light photocatalytic properties of BiOCl0.2Br0.1I0.7 were investigated for the first time. Powder samples were characterized by XRD, SEM, UV-vis spectrophotometry and nitrogen sorption. BiOCl0.2Br0.1I0.7 absorbs intensely in the visible light region and the optical bandgap is 1.82eV. The chlorine and the bromine elements have an obvious effect in changing the bandgap energy and the particle size of the catalysts. The deep valance band edge position, the internal electric ﬁelds and the morphology give the BiOCl0.2Br0.1I0.7 best visible light photocatalytic properties.