Mn-doped ZnS nanoparticles, having average diameter 3-5 nm, have been synthesized using chemical precipitation technique without using any external capping agent. Zinc blende crystal structure has been confirmed using the X-ray diffraction studies. The effect of various concentrations of Mn doping on the photoluminescent properties of ZnS nanoparticles has been studied. The time-resolved photoluminescence spectra of the ZnS:Mn quantum dots have been recorded and various parameters like lifetimes, trap depths, and decay constant have been calculated from the decay curves at room temperature. The band gap was calculated using UV-Visible absorption spectra.