Activated carbon has been synthesized by a high-temperature annealing route using graphite as carbon source and potassium hydroxide as the etching agent. Many nanosized carbon sheets formed on the particles could be of benefit for rapid intercalation/de-intercalation of potassium ions. Moreover, the d-spacing in the (100) crystal planes of the as-prepared active carbon is enlarged to 0.335 nm, even some formed carbon nanosheets can reach 0.358 nm, and the diffusion coefficient of K ion is also improved by 7 times as well. The as-prepared activated carbon electrode can deliver a high reversible capacity of 100 mAh g ¿1 after 100 cycles (at a high current density of 0.2 A g ¿1 ), and exhibits increased rate performance. The results demonstrate that the as-prepared active carbon is a promising anode material for the potassium ion battery, with high capacity, excellent rate performance, and great cycling stability.