Ethylene (E), propylene (P), and 1,4-hexadiene (HD) were terpolymerized with rac-1,2-ethylenebis (1-eta(5)-indenyl) zirconium(IV) dichloride and methylaluminoxane (Et[Ind]2ZrCl2/MAO), and compared with the copolymerizations of E/P, E/HD, P/HD, and terpolymerization using ethylidene norbornene (ENB) as the termonomer. HD lowers the polymerization activity, the effect is more pronounced for P/HD and E/P/HD using large amount of P, than for E/HD and E/P/HD using feed low in P. The polymer molecular weight is most strongly affected by the temperature of polymerization (T-P), whereas the E/P ratio in the feed has virtually no effect. The reactivity ratios r(E) and r(P) are 3.0 and 0.3, respectively, at 20 degrees C but r(P) becomes larger than r(E) at T-P = 70 degrees C. H-1-NMR spectra showed occurrence of cycloaddition in the homopolymerization of HD; on the other hand, HD is incorporated in the terpolymer only by linear 1,2-addition.