CoMn₂O₄ nanoparticles on reduced graphene oxide (CoMn₂O₄/rGO) composites with different graphene contents were synthesized in situ by a coprecipitation method. The effect of graphene content on the morphology, microstructure and electrochemical properties of CoMn₂O₄/rGO materials was investigated. The results show that CoMn₂O₄ nanoparticles are deposited on the surface of graphene nanosheets. The distribution of CoMn₂O₄ nanoparticles on the surface of rGO is gradually uniform, and the particle aggregation disappears as graphene content increases. CoMn₂O₄/rGO exhibits a great specific surface area and an excellent electrochemistry. The optimum capacitance performance of CoMn₂O₄/rGO20 (20% rGO, in mass fraction) can be obtained, and the specific capacitance is 1 420 F/g at 1 A/g. CoMn₂O₄/rGO30 (30% rGO, in mass fraction) has the optimum cyclic stability. The specific capacitance retention rate of CoMn₂O₄/rGO30 is 94% at 5 A/g, while that of CoMn₂O₄ is 78%, after 2 000 cycles of charges and discharges.