Kinetics of the formation of polyurethane (PU) prepolymer (PP) between isophorone diisocyanate (IPDI), polycarbonate glycol (PCD), and dimethylol propionic acid (DMPA) were studied by using quantitative in-situ IR spectroscopy. Urethane reaction was followed by monitoring the change of intensity of absorption band at 2,270 cm(-1) for NCO stretching in IR spectrum. In our's results, the reaction kinetics in PP formation was shown to obey first- order kinetics up to about 50 % conversion. The activation parameters were obtained from the evaluation of kinetic data at different temperatures, 60 ℃, 65 ℃, and 75 ℃. The activation energy was found to be Ea=24.66 kJ/mol.