A porous reduced graphene oxide, with a Brunauer-Emmett-Teller surface area of up to ~ 3120 m² g^-1, is prepared by using chemical activation of microwave exfoliated graphite oxide. The sp²-bonded carbon has a continuous three-dimensional network of highly curved atom-thick walls with ~ 1 to 5 nm width pores. As an anode material for lithium ion battery, it can deliver a reversible specific capacity of 1603.4 mAh g^-1. To understand the Li storage mechanism, the porous carbon samples with specific surface area tunable are investigated. The high reversible capacity indicates that the meso- and micropores are the key factor for Li insertion/extraction during discharge and charge. The porous structure and large specific surface area is believed to have contributed to the high performance.