The kinetics of propylene polymerization with Et(H(4)Ind)(2)ZrCl2/methylalumoxane (MAO) catalysts have been investigated at 0-50 degrees C and 1 atm of propylene pressure. The effects of polymerization temperature, catalyst concentration, and catalyst/cocatalyst mole ratio on the catalyst activity and on the properties of the polypropylene products were studied. By assuming the coexistence of two dynamic equilibria between catalytically active species and two inactive species, which are the products of zirconocene dimerization and excessive zirconocene-MAO complexation, a kinetic model has been developed. This model could satisfactorily explain most of experimental results.