Photocatalysis is a green technology which transforms available photon energy into useful chemical energy. The reaction mechanism is based on the ability to create electron–hole pairs under appropriate light. Semiconductors have attracted great attention in photocatalysts because of their high photosensitivity. Spinel–type cobalt oxide nanorods have been prepared by a simple hydrothermal method using cobalt nitrate as precursor. Sn-doped Co3O4 was composited with carbon nanotubes for better photocatalytic activity. An extensive characterization of the prepared samples was carried out using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), Vibrating sample magnetometer (VSM) and UV–Visible absorption spectroscopy. The XRD results show the formation of Co3O4 phase with FCC structure, FESEM confirms the nanorods morphology of the cobalt oxide and the VSM taken at room temperature shows an antiferromagnetic behavior. The investigation of photocatalytic activity of Co3O4 based was done by methyl orange dye. At the end, the responsible mechanism of CNT/Sn–CO was discussed.