The catalytic effect of Fe(AA)₃ on polymerization of HTPB-IPDI system was investigated. It was found that the reaction of HTPB-IPDI system obeys the pseudo-second order reaction law and the dependence of the rate constant on Fe(AA)₃ concentration is parabolic while the addition of small amounts of acetylacetone (HAA) to the Fe(AA)₃ catalyzed reaction causes a hyperbolic response. The experimental results obtained are as follows: (1) In both cases of low molecular weight alcohol-isocyanate system and high molecular alcohol-isocyanate system, the reaction obeys the Bruenner''s mechanism. (2) Activation energies of HTPB-IPDI system are 13.63 kcal/mole for uncatalyzed reaction and 12.57 kcal/mole for Fe(AA)₃ catalyzed reaction.