This book is briefly describe the luminescence phenomenon of CdS:Mn nanoparticles. The absorption Spectra and band gap measurement, particle size calculation by effective mass approximation and hyperbolic band model. Preparation of CdS nanocrystals of various sizes by chemical precipitation technique using different concentration of capping agent at different temperature. The variation of temperature effect in synthesis process of Mn doped CdS samples. Optical studies of CdS:Mn nanoparticles and concentration effect of capping agent with molar change in Mn percentage.