The tritiated alcohol quench method has been used for determining the number of active centers in the polymerisation systems of Nd compounds-A1 (i-Bu)₂Cl-A1Rsub>3-butadiene.The number of active centers in this polymerization systems has been shown to lie in the range of 0.004-0.08 mol/mol Nd for catalytic systems in which five neodymium compounds and two aluminium alkyls reacted with each other.In the present study the influence of polymerization condition and catalyst composition on active centers and propagation rate constants were investigated.The data obtained show that the propagation rate constant does not depend on the nature of A1R₃ and Nd compounds.Thus,it can be concluded that the difference observed in catalyst activities is related to the number of active centers formed.