Cobalt-nanoferrite as a magnetic separable material has drawn the attention of researchers due to its unique properties, significant applications and high potentiality in wastewater treatment. In this study, the cobalt nanoferrite was synthesized by chemical co-precipitation method at different annealing temperatures and characterized by X-ray diffraction, scanning electronic microscopy, energy dispersive X-ray, Fourier transform infrared spectroscopy and UV-visible spectroscopy. Then the synthesized nanoferrite was assessed and used for the treatment of tannery wastewater. The characterizations confirmed the formation of nanoferrites with size between 15 and 23 nm. The average particle size increased with increase of annealing temperatures. Typical values for tannery wastewater treatment efficiency for chromium, total dissolved solids, biochemical oxygen demand and chemical oxygen demand were 23.75, 90.83, 52.72 and 48.07% respectively. Thus, the treatment by nanoferrites appears a promising and effective method for the removal of contaminants.