In this paper, the nanocomposites of reduced graphene oxide/lanthanum oxide are prepared by a simple reflux process. The reduced graphene oxide with a large specific surface area is successfully decorated with lanthanum oxide. The reduced graphene oxide/lanthanum oxide composites are fabricated as the electrode material in a supercapacitor device which displays a high specific capacitance of 156.25 F/g at a current density of 0.1 A/g and excellent cycle stability. The material keeps 78% of its initial charge-discharge efficiency after 500 cycles. The excellent electrochemical performance of composite material may be attributed to the deposited lanthanum oxide nanoparticle on the surface of reduced graphene oxide, which increase the effective conductive area of reduced graphene oxide and the contact area between electrolyte and graphene. The graphene-lanthanum oxide composites can significantly improve the stability and electrical performance of supercapacitors and has great potential in chemical sensors, microelectronics, energy storage and conversion applications.