Reduced graphene oxide/Mn3O4 (RGO/Mn3O4) nanocomposites were synthesized via a cost-effective approach, and their microstructural and morphological features were investigated. Field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) results revealed that the Mn3O4 nanoparticles were crystallized with particle size 50–100nm while the size of the Mn3O4 particles in RGO/Mn3O4 composites decreased to 30–50nm, suggesting that RGO promoted the dispersion of Mn3O4 particles. We tested the electrochemical behavior of the RGO/Mn3O4 composites for supercapacitor and Li-ion battery. And it was found that they exhibited an excellent discharge specific capacitance of about 194.8F/g at 1.0A/g with 90% capacity retention even after 1000cycles in supercapacitor, and an initial discharge capacity of about 1813mAh/g at 0.1A/g with outstanding cycling stability in Li-ion battery.