In this paper, we analyzed the structural and optical properties of quaternary semiconductor Cu2ZnSnSe4 (CZTSe) thin film. For this purpose, the structural properties of CZTSe thin film were analyzed using X-ray diffraction (XRD) and transmission electron microscopy (TEM). CZTSe nanocrystals (NCs) were formed in the kesterite phase and with good crystallinity. Optical characterization of thin film was investigated using spectroscopic measurements. Optical parameters of CZTSe film coated using the spin coating technique were determined by UV-Vis-NIR spectroscopy. The refractive index, extinction coefficient, and dielectric constant of the thin film were calculated using transmittance and reflectance data. Moreover, dispersion parameters such as oscillator energy, and dispersion energy were obtained by the Wemple DiDomenico model. For CZTSe film in the visible wavelength region, the transmission has values of 70–75%. The thin film of CZTSe has a direct band gap of 1.4 eV which is suitable for absorbed layer for solar cell.