The effect of Cr doping on dielectric and optical properties of ZnS nanoparticles was systematically investigated at room temperature. Structural analysis confirmed that dopant occupy the regular lattice and interstitial sites in host lattice. Experimental data revealed exceptionally large, low frequency dielectric constant (epsilon' approximate to 10(6)) and enhanced photoluminescence emission in Cr doped ZnS nanoparticles. It is argued that larger value of the dielectric constant in doped nanoparticles originate due to combined effect of MaxwellWagner phenomenon and microscopic spontaneous polarization, when larger ionic radius Zn2+ (0.74 angstrom) ions are replaced by smaller ionic radius Cr3+(0.63 angstrom) ions. The huge enhancement in the value of dielectric constant and emission intensity justify the use of doped ZnS nanostructures for various technological applications. (C) 2017 Elsevier B.V. All rights reserved.