This paper presents the results from a study related to the effect of solution pH on particle size and photocatalytic properties of ZnS nanoparticles (NPs). ZnS NPs capped with 2-Mercaptoethanol (2-ME) have been synthesized via chemical precipitation route at different pH values, i.e., 8, 10, and 12. Effect of solution pH on particle size of NPs has been studied by the Dynamic Light Scattering (DLS) technique. A comparison of the results obtained from the DLS technique for ZnS NPs synthesized at different pH values showed narrower particle size distribution as we go from higher pH value, i.e., 12, to lower pH value, i.e., 8. Fourier Transform Infrared Spectroscopy (FTIR) has been carried out to study the presence of hydroxyl groups and 2-ME on the surface of NPs. Comparative photocatalytic study of these NPs has also been carried out using Ponceau S dye.