Cu2ZnSn(S,Se)4 (CZTSSe) is a compound semiconductor which replaces a part of S in the CZTS crystal by Se. The bandgap varies from 1.05 eV to 1.51 eV depending on the mole ratio between S and Se. In this paper, CZTSSe thin films were prepared by the selenidation of CZTS film, and the Se mole ratio was tuned by changing annealing conditions. The film quality of the obtained CZTSSe was characterized by X-ray diffraction (XRD) and Hall measurements. It was revealed that both the supply of Se vapor pressure and the annealing temperature of CZTS were controlling parameters for the selenidation of the film. The crystal quality of CZTSSe was also influenced by the supply of Se vapor pressure.