In the present investigation, Cu x Co 3- x O 4 ( x = 0, 0.02, 0.04, 0.06, 0.1) nanoparticles have been synthesized by the sonochemical method and subsequent calcination at high temperature. The synthesized nanoparticles were further characterized using X-ray diffraction, UV-vis spectroscopy, FT-IR spectroscopy, Raman spectroscopy, transmission electron microscopy and energy-dispersive X-ray spectroscopy. The analysis results showed that nanoparticle size, band gap and photocatalytic activity of Cu x Co 3- x O 4 compounds change by altering the Cu doping content. According to the XRD study, no impurity peaks associated with copper or copper oxide phases were observed in the diffractograms of doped samples. The highest degradation of methylene blue dye under visible light was observed in the presence of Cu 0.02 Co 2.98 O 4 nanoparticles and found to be 87.51% after 330 minutes. This value increased with increasing the amount of photocatalyst and with decreasing dye concentration., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)