The LiFePO4/C composites with different morphology are synthesized by an ammonia assisted hydrothermal method at various ammonia concentrations (from 0 to 1.6molL−1) using inexpensive Fe(NO3)3 and LiOH as raw materials. The influences of the ammonia concentration on the structure, morphology and electrochemical properties of the LiFePO4/C composite are investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), galvanostatic charge/discharge tests and electrochemical impedance spectroscopy (EIS). The results demonstrate that the ammonia concentrations markedly impact the morphology and electrochemical properties of the LiFePO4/C. With the change of ammonia concentrations, the LiFePO4/C synthesized with 0.4molL−1 ammonia shows the smallest average particle size, the most uniform microsphere particle distribution and relatively high tap density (1.27gcm−3). In addition, the sample appears a high discharge capacity of 153.9mAhg−1 at the first cycle as well as stable cycling performance (the capacity was not almost changed till 100 cycles) at a rate of 1C (170mAg−1). Moreover, it exhibits a good rate capability and still shows a high discharge capacity of over 125mAhg−1 even at a rate of 5C.