Mn(IV) or Mo/(VI) substituted single phase compounds having a nominal composition Li1+yMnyV3-yO8(0 < y < 0.1) and LiMoyV3-yO8 (0 < y < 0.3), respectively have been obtained by solid-state reaction, Electrochemical measurements revealed different influences of substitution on the lithium insertion behaviours. While substitution of V(V) with Mn(IV) and introduction of Li(I) into the interlayer decrease the insertion limit of lithium, substitution of V(V) with Mo(VI) shows a featureless discharge curve without changing the insertion limit. The ionic sites available for Li+ occupation between the layers rather than the electronic sites offered by V(V are considered to determine the insertion Limits of lithium into Li1+xV3O8.