Photoconductivity of Cd1+y(SxSe1−x) single crystals with controlled deviation from Stoichiometry is studied. The deviation y from Stoichiometry of the sample is controlled through the growth process or a heat treatment by regulating the sum of chalcogen partial pressure Pps ( = Ps2 + Pse2), and by keeping the pressure ratio Pr (= Ps2/Pse2 constant in each experiment. The photoconductivity at room temperature and 85 K of high resistivity samples decreases rapidly with increasing Pps. From the results, it is found that the native defect such as Cd vacancy is created in the crystal through the Stoichiometry control and its electrically neutral state acts as a recombination centre for photoconductivity.