Fine-sized, well-crystallized LiMnPO4 and two Cu-doped derivatives (2% and 5% Cu2+ doping) are readily prepared via a hydrothermal route. X-ray diffraction (XRD) combined with structural analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), specific surface area analysis, and galvanostatic charge–discharge tests are applied to characterize these materials. The structure analysis shows that only a negligible amount of Cu2+ ions (0.2%) occupy the Li sites in the 2% Cu-doped material, while a considerable amount of Cu2+ ions (1.8%) occupy the Li sites in the 5% Cu-doped one. The electrochemical tests show that the 2% Cu-doped LiMnPO4 displays an improved electrochemical performance compared with the undoped LiMnPO4, while the 5% Cu-doped LiMnPO4 exhibits a decreased activity.