The structural, electronic and optical properties of CaxZn1-xS in B3 phase are investigated in order to see the effect of addition ofCa in ZnS in the range 0ï£ ï´ ï£1. For this purpose, first principle density functional calculations, using full potential linearized augmented plane wave (FP-LAPW) method, have been used. The equilibriumstructural parameters for CaxZn1-xS are obtained fromthe total energyminimization calculationswith respect to volume. The electronic structure and the density of states for CaxZn1-xS are calculated and analyzed in terms of the contribution of Zn s and d, S s and Ca p and d states. Optical properties such as complex dielectric constants (ï¥), refractive index (n), extinction coefficient (k), normal-incidence reflectivity (R), absorption coefficient (ï¡), and optical conductivity (ï³), are also calculated and analyzed in the incident photon energy range 0-50 eV. It is found that the direct bandgap ï ïïï g varies from2.2 eV to 3.7 eV as x varies from0 to 1 and the optical properties of CaxZn1-xS also changes accordingly.