The kinetics of the polymerization of isoprene with Nd(naph)3-Al(i-Bu)3-Al2 (C2H5)3Cl3 catalyst system has been studied in heptane in the temperature range of 20-50℃. The polymerization rate was found to be first order and 1.7 order to monomer and catalyst concentration respectively and the observed activation energy for the polymerization is 9.0 kcal/mole. Based on above mentioned results a mechanism of catalyst formation was proposed. Data obtained in the polymerization of isoprene with successive addition of monomer indicate that there is no deactivation of active centers in the studied temperature range. Effects of the polymerization conditions on the intrinsic viscosities of polymer were also investigated.