Ferrous oxalate was employed as iron source to synthesize LiFePO4 (i.e., a cathode material for Li-ion batteries) via a hydrothermal route. XRD and FESEM were used to analyze the structure and texture features of products, while coin-cell charge/discharge tests were conducted to measure the electrochemical performance of products. Conditions for hydrothermal crystallization were optimized. The results demonstrate following information: The temperature of 190℃ is the minimum feasible crystallization temperature. The crystallization time for hydrothermal synthesis should be shorter (e.g., 10 h) rather than longer (e.g., 24～57 h), because a long crystallization time may cause the LFP’s relative diffraction intensity to deviate the standard XRD pattern, which is a sign for structural change, as well as the huge disparity of particle sizes. As the crystallization temperature for hydrothermal synthesis reaches 280℃, a part of Fe(II) within the carbon-free product may be oxidized to Fe(III) and form FePO4•2H2O impurity, while an addition of glucose (i.e., a carbon source) may suppress the conversion from Fe(II) to Fe(III). LiFePO4 with less-aggregated particles and a specific discharge capacity of 154 mAh/g may be hydrothermally synthesized at suitable crystallization temperature (e.g., 240～260℃) and time (e.g., 10 h) using ferrous oxalate as the iron source, which consumes 6339 mol of lithium source (LiOH) compared with 19016 mol consumed by the hydrothermal method using ferrous sulfate.