The hard carbon is attractive for the Li ion secondary battery because of its higher capacity than the theoretical value of 372Ahkg−1 based on the composition of stage 1 Li-intercalated graphite, LiC6. However, the structure of hard carbon as an anode has not been optimized and the reaction mechanism also has not been clarified in detail. In the present study, the structure of hard carbon derived from oxygen-containing coal tar pitch was investigated by X-ray diffraction, small angle scattering and density measurement, and the relationship between the structure of hard carbon and its anode performance was discussed.