LiMnPO4/C samples synthesized by two different methods are characterized by physical and electrochemical measurements and the importance of porosity on the electrochemical activity is investigated. The LiMnPO4/C synthesized by solid-state route has porous micro-aggregates while the micro-aggregates of the LiMnPO4/C synthesized by wet-chemistry route are dense. The difference in porosity of the two samples leads to a significantly different electrochemical activity. When cycled at the rate of 0.1C, the sample synthesized by solid-state route can deliver a capacity of 121mAhg−1, while the sample synthesized by wet-chemistry route can only deliver a capacity of 36mAhg−1. Our result demonstrates that the formation of sufficient pores in the aggregates is essential to achieve high electrochemical activity for LiMnPO4 based material.