A series of Li1-xNaxV3O8 (0 < x < 1) solid solution were investigated as positive materials for secondary lithium batteries, The materials were characterized by X-ray diffraction and infrared spectrum measurements : showing that pure phases of Li1-xNaxV3O8 were formed with the same monoclinic structure as LiV3O8. The electrochemical characteristics including charge-discharge characteristics were compared with those of LiV3O8 and NaV3O8, showing that the Li0.7Na0.3V3O8 electrode shows the best electrochemical performance among several Li1-xNaxV3O8; at a current density of 0.2 mA cm(-2), it gave a discharge capacity of 215 mAh g(-1)-oxide which was about 80% of the theoretical discharge capacity. The cathode current loading test also showed that Li1-xNaxV3O8 has the advantage of both LiV3O8 and NaV3O8. Furthermore, the thermodynamics and kinetics of lithium intercalation into the oxide structure were also examined.