This work demonstrates the preparation of Cu2ZnSn(SxSe1-x)4(CZTSSe) thin films by sputtering deposition using single-phase Cu2ZnSnS4 (CZTS) target followed by selenization/sulfurization treatment at 570 °C for 1 h. Afterward, the CZTSSe thin-film solar cell samples with the Mo/CZTSSe/CdS/i-ZnO/IZO/Al structure were prepared and their performances were evaluated. By varying the ratio of Se and S powders of heat treatment, the Cu-poor/Zn-rich CZTSSe layers with S/(S+Se) ratio in the range of 0.21–1 were achieved and the CZTSSe layers were the mixture of kesterite CZTS and CZTSe phases as revealed by the x-ray diffraction and the Raman spectroscopy analyses. UV-NIR spectroscopy indicated the bandgaps of CZTSSe samples are in the range of 1.06–1.45 eV when the S/(S+Se) ratio varies from 0.21 to 1. Hall measurement observed the best transport property with p-type carrier concentration of 2.17×1015 cm−3 and mobility of 8.9 cm2 V−1 sec−1 in CZTSSe layer with S/(S+Se) ratio of 0.46. Under the AM1.5 illumination condition, the CZTSSe thin-film solar cell sample with S/(S+Se) ratio of 0.46 exhibited the best performance with open-circuit voltage of 0.506 V, short-circuit current density of 27.41 mA/cm2, fill factor of 50% and conversion efficiency of 6.9%.