Abstract : A cytocompatible silica-zinc catalyst from cow dung for photocatalytic reduction of Chromium (VI) to Chromium (III) was prepared by sol-gel method with zinc nitrate and the sodium silicate solution prepared from the cow dung ash. The catalyst was characterised by X-Ray Diffraction (XRD) analysis, which indicated the Opaline form (Opal-C) of silica. This result was further corroborated in the Infrared (IR) spectrum. Silicon, Sodium, and Zinc were confirmed using an energy-dispersive spectrum, and the surface morphology indicated agglomerated particles and hollow tubular structures of different dimensions in the Field emisson scanning electron microscopy (FE-SEM). The direct band gap of 4.9 eV was calculated from diffuse reflectance studies. The Chromium (VI) to Chromium (III) reduction was analysed by DPC complexation and absorbance at 540 nm in a UV–visible spectrophotometer. MTT assay test proved that the composite is cytocompatible with more than 50 % cell viability even at higher concentrations like 100 µg/mL.