Abstarct: In this work, electronic and optical properties of CdS compound in the bulk form were investigated using Density Functional Theory (DFT).calculation was prformed using Quantom espresso software and ultrasoft pseudoptential. calculation were done by LDA and GGA approximations. After initial optimization, total particle density of states and band structure for the compound were calcuted. In optical studies, the band gap energy, dielectric functiones, absorption, optical conductivity, refractive index, extinction coefficient, energy lost and reflectivity were investigated. The obtained density of states showed that the lower part of the conduction band (near the Fermi level), composes of the Cd:s, p states and the edge states of valance band contains S:3p. The result showed that the band gap calculated by the GGA approximation is closer to the experimental value than LDA approximation.