We investigated sodium/pyrite battery because sodium and pyrite (natural FeS2 ore) were very cheap materials. The sodium/pyrite battery showed high discharge capacity of 630 mAh g(-1)-FeS2 with 50 mA g(-1)-FeS2 at room temperature, which was higher than that of Li ion battery and Na/synthetic FeS2 battery. First discharge curve had one plateau-shaped voltage region of 1.3 V, which disappeared and changed to sloping shape after second cycle. The discharge capacity decreased continuously by repeated charge-discharge cycling, and remained 85 mAh g(-1)-FeS2 after 50th cycles. (C) 2007 Elsevier B.V. All rights reserved.