Li2MnO3 is an important component of the Li-rich Mn-based high-capacity cathode material for lithium ion batteries, xLi2MnO3·(1 − x)Li M′ O2 composites. Replacing Li2MnO3 with iso-structured Li2MoO3 is expected to improve the rate performance and suppress the oxygen release of the composites at high potentials due to the higher electric conductivity of Li2MoO3 and its more facile charge compensation (by Mo4+/Mo6+ redox) upon Li removal than that of Li2MnO3. As part of our series work on the Li2MoO3-based Li-rich layer structured cathode materials, this article is to study the structural and performance stability of Li2MoO3 in air. The obtained information will shed light on the development and application of xLi2MoO3·(1 − x)Li M′ O2 composite cathode materials though Li2MoO3 will not be applied as an independent cathode material.