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 630mAhg−1-FeS2 with 50mAg−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 1.3V, which disappeared and changed to sloping shape after second cycle. The discharge capacity decreased continuously by repeated charge–discharge cycling, and remained 85mAhg−1-FeS2 after 50th cycles.