The formation reaction of LiFePO4 from decomposition of precursors LiOH, FeSO4.7H2O and (NH4)2HPO4 with mole ratio of Li:Fe:P=1:1:1 was investigated. The experiment was carried out by thermogravimetric differential thermal analysis (TG-DTA) method using nitrogen as atmosphere at a constant heating rate to obtain kinetic constant parameters. Several heating rates were selected, viz. 5, 7, 10, 15, 17.5, 22.5 and 25 °C min-1. Activation energy, pre-exponential factor and reaction order were taken using Kissinger method and obtained 56.086 kJ/mol, 6.95×108 min-1, and 1.058, respective-ly. Based on fitting result between reaction model and experiment were obtained that reaction obeyed the three dimension diffusion model.