An eco-efficient approach bases on a mechano-chemical liquid-phase activation technique is developed for synthesizing LiMnPO4/C composites. The fine sized [Mn3(PO4)2·xH2O + Li3PO4] precursors with uniform particle size distribution are prepared, and characterized by XRD and scanning electron microscope (SEM). The in—situ carbon coated LiMnPO4 composites are synthesized by one-step solid state reaction. The prepared LiMnPO4/C nano-composites show a comparable rate capability with discharge specific capacity of 136.4 mAh g−1 at 0.05 C-rate and 118 mAh g−1 at 1 C-rate at room temperature. The results indicate that LiMnPO4/C composites synthesize from this environmental friendly route shows a promising electrochemical activity as cathode material for lithium ion batteries.