Semiconductor nanoparticles exhibit effects of quantum confinement of electrons and holes in dictating optical and electronic properties. One can thus tune the band gap by changing the particle size. As the Optical properties are strongly dependent on particle size, a particle size distribution is expected to cause inhomogeneous broadening of optical spectra. Nanocrystalline materials exhibit a variety of properties that are different and often considerably improved in comparison with bulk materials. These include increase strength, enhanced diffusivity, improved ductility/ toughness, reduced density, reduced elastic modulus, higher electrical resistivity and superior soft magnetic properties in comparison to bulk crystals. Luminescence which is an optical property is enhanced if the size of any particles is reduced up to nano -size. As the wavelength of light gets reduced. The present theoretical work is devoted to the Study of Broadening in the Photoluminescence peaks with variation in particle size of (ZnS, CdS) nanocrystals.