ZnIn 2 Se 4 has a polycrystalline structure in as synthesized condition. It transforms to nanostructure grains of ZnIn 2 Se 4 upon thermal deposition as thin films. The optical properties of as deposited ZnIn 2 Se 4 films are studied using spectrophotometer measurements of transmittance and reflectance at normal incidence of light in wavelength range (450-2500) nm. The refractive index and absorption index are calculated and it is found that they are independent of film thickness in the thickness range (500-790) nm. Absorption analysis showed two types of electronic transitions; indirect allowed transition with energy gap 1.76 eV accompanied by phonon of energy 25 meV and direct allowed transition with energy gap 2.3 eV. The dispersion analysis showed that the oscillator energy, dispersion energy, dielectric constant at infinite frequency and lattice dielectric constant are 2.49 eV, 14.36 eV, 6.84 and 8.17, respectively.