In this project work energy band gap (Eg), particle size (D), dislocation density(ρ), and refractive index (n) of Cu:ZnS nanoparticles with concentration 0.05M,0.1M,0.15M, and 0.2M are calculated. These Eg, D, and ρ are calculated with Brus equation. And n is calculated by Moss relation. The effect of temperature on Cu:ZnS nanoparticles is also detected. It is noticed that temperature and Cu concentration behaves oppositely to Cu:ZnS nanoparticles. When temperature increases, energy gap decreases, while increases concentration, increases energy gap. The calculated band gap values range from 3.14eV for pure ZnS to 3.52eV for the Cu:ZnS sample with a 0.2M concentration. The calculated particle size decreases with the increase in copper concentration, from 5.9 nm for Cu:ZnS (0.05M) to 3.5 nm for Cu:ZnS (0.2M). As the copper concentration in the Cu:ZnS samples increases, the refractive index decreases, ranging from 2.338 for the 0.05M sample to 2.284 for the 0.2M sample. For pure ZnS, the dislocation density is approximately 1.71 × 1010 m -2 , while for the Cu:ZnS(0.2 M) sample, the dislocation density is around 9.82 × 1010 m -2 .