Kinetics of pre-polymerization of polyurethane formation between isophorone diisocyanate (IPDI) and dimethylol propionic acid (DMPA) in solution state (IP reaction), and IPDI and dimethylol butanoic acid (DMBA) in solution state (IB reaction) were studied by using quantitative real-time in-situ IR spectroscopy at different temperatures in the range of 60-90 ℃ with [NCO]/[OH] ratio of 1.0. The reaction rate was obtained from monitoring the change of NCO (2,265 cm^-1) stretching band in series IR spectra. The reaction was in accord with the first-order for the concentrations of hydroxyl groups and isocyanate groups respectively, which conformed to the second order law entirely. The activation parameters were obtained from the evaluation of kinetic data as follows. For IP reaction, activation energy (E_a)=42.2 kJ/mol, activation enthalpy (ΔΗ^‡)=39.3 kJ/mol and activation entropy (ΔH^‡)=-146.7 J/mol K. For IB reaction, E_a=36.9 kJ/mol, ΔH^‡=34.0 kJ/mol and ΔS^‡=-163.3 J/mol K.