[en] In the present work, Co₃O₄, 1% chromium doped Co₃O₄ (1 % Cr:Co₃O₄), and 5% chromium doped Co₃O₄ (5 % Cr:Co₃O₄) was successfully prepared by simple chemical method followed by calcination at 400°C for 3 hrs. The synthesized nanoparticles materials were characterized by XRD, SEM, EDX, Brunauer Emmett Teller analysis (BET), and UV-visible spectroscopy. XRD confirmed the formation of cubic nature of nanoparticles while SEM images shown spherical structure. BET analysis confirmed the mesoporous behaviour of nanoparticles. UV-Visible spectra have been used to determine band gap and photo-oxidation behaviour of organic dye methyl orange. Experimental data suggested that 5% Cr:Co₃O₄ nanoparticles catalyst possessed the highest catalytic activity towards MB degradation in aqueous solution at the tested concentration level of 50 mg/L, higher than that of pure Co₃O₄. Complete decolourization of the 50 mg/L MB solution can be achieved by 5% Cr:Co₃O₄ nanoparticles within 35 min in the presence of visible light irradiation. (author)