Thermal and mechanical properties of ethylene-propylene-a-olefin (a-olefin: I-hexene, 1-decene, and 1-octadecene) terpolymers, obtained with the metallocenic system rac-Et[Ind](2)ZrCl2/MAO with different comonomer ratios, have been studied. The properties were related to the terpolymer composition and molecular weights. Mechanical behavior of terpolymers was much more influenced by propylene than by alpha-olefin contents. (c) 2007 Wiley Periodicals, Inc.