The synthesis and characterization of Co₃O₄ nanoparticles via solid state thermal decomposition of a binuclear cobalt(III) complex, as a new precursor is reported. Solid state thermal decomposition of the complex at 450 °C for 3 h produces Co₃O₄ nanoparticles which are characterized by FT-IR spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). SEM and TEM images exhibit the quasi-spherical shape of the Co₃O₄ nanoparticles of between 20 and 30 nm. Moreover, adsorption of methylene orange dye on Co₃O₄ nanoparticles was investigated and the uptake% was determined to be >45% in 200 min.