The present work outlines the importance of biosynthesized selenium nanoparticles (SeNPs) as co-catalyst for the enhanced photocatalytic activity of as -prepared ZnS photocatalyst for degradation of methyl orange (MO) dye under IN light irradiation. SeNPs of different wt% were impregnated onto ZnS by calcination at 200 degrees C to make Se-ZnS nanocomposites (Se-ZnSNCs) and characterized by UV-Vis spectroscopy, DLS, XRD, SEM-EDX, TEM and BET surface area analysis. The specific surface area notably increased from 54 m(2) g(-1) (ZnS) to 75 m(2) g(-1) with different wt% of Se loading. The band edge absorption at 330 nm (3.77 eV) of bare ZnS significantly red -shifted to 357 nm (3.30 eV), after 1 wt% Se loading (3.30 eV). 1 wt% Se-ZnSNCs exhibited the highest degradation efficiency (95%) of MO as compared to bare ZnS (55%) under 160 min UV light irradiation. The reaction followed pseudo first -order kinetics with an apparent rate constant k = 8.42 x 10(-3) min(-1) where CO2 evolution gradually increased depending on the extent of MO degradation by Se-ZnSNCs under different time period of UV light irradiation. (C) 2016 Elsevier B.V. All rights reserved.