The effects of structural modification caused by substitution of Mo for a part of V in V2O2 on structural changes upon lithium insertion were investigated. For this purpose (V1−y Mo y )2O5 (y=0.25) was synthesized, and its insertion behavior and structural changes upon lithium insertion were analyzed by XRD and ESR methods. In (V0.75Mo0.25)2O5, the phases except for the starting material were not observed upon lithium insertion, and no phase transformation characteristics of V2O5 occurred. From ESR measurement, a broad singlet signal of V(IV) was found, but those of Mo(V) were not detected. The line width of the signal V(IV) increased steeply at 0.7<x<1. The open circuit potentials became less noble with increasing x, and dropped steeply at 0.7<x<1. These dependencies closely correlate with structural changes estimated from results of ESR and XRD analyses. At 2.7<x, ω-phase oxide was formed.