Herein, pure ZnS and Sn-doped (1–5 wt%) ZnS nanoparticles (NPs) were prepared by simple chemical co-precipitation method. The average crystallite sizes of synthesized NPs determined using Debye–Scherrer formula were found to be between 3 and 5 nm. Morphological features of ZnS NPs were determined by field emission scanning electron microscopy (FE-SEM). The microscopy result showed that the samples had microspherical structure and were assembled by tiny particles. UV–Vis studies were performed for the determination of bandgap of the samples. The compositional information of photocatalysts was determined by energy-dispersive X-ray spectroscopy. Photocatalytic activity of NPs was evaluated by taking methylene blue (MB) and methyl orange dyes as model pollutants and their comparative degradation behavior has been discussed. The Sn-doped ZnS NPs displayed excellent photodegradation efficiency of 93% for MB dye compared to 49% for ZnS.