Electrochemical lithium insertion/extraction reaction on three MoO3 samples with different crystallinity, which were heat-treated at 300, 600, and 750 degrees C, was studied, and the structural change of the host MoO3 during the lithium insertion/extraction process was followed by XRD measurements on the oriented cathode plates in a reflection and transmission arrangement. The possibility of the insertion of solvated lithium ions into the van der Waals gap and of the accommodation of some of the lithium ions into the sites in the Mo-O octahedron layers were expected. A scheme of lithium insertion into crystalline MoO3 was discussed.