We investigated the structural stability and electrochemical properties of LiMnBO3 in the hexagonal and monoclinic form with ab initio computations and, for the first time, report electrochemical data on monoclinic LiMnBO3. In contrast to the negligible Li-storage capacity in the hexagonal LiMnBO3, a second cycle discharge capacity of 100 mAh/g was achieved in the monoclinic LiMnBO3, with good capacity retention over multiple cycles. Elevated temperature cycling indicates that the capacity of monoclinic LiMnBO3 is kinetically limited, and further improvement may be expected by addressing the Li ion and/or electron transport limitations.