A high-activity Ziegler-Natta catalyst of TiCl4-supported MgCl2 (ethoxide type) was prepared. Ethyl benzoate (EB) and polydimethylsiloxane PDMS) were used as internal donors, while p-methyl toluate (MPT) and triethylaluminum (TEA) were used as the external donor and cocatalyst, respectively. Suspension copolymerization of ethylene-propylene (EPM) was carried out in n-heptane using the catalyst system. The relative pressures of 1.5 : 1 and 2 : 1 atmosphere of propylene-to-ethylene (PIPE) gave a polymer with elastomeric properties. The relative pressure of propylene-to-ethylene higher and lower than the above values, however, gave a homopolymer or copolymer without elastomeric properties. The effect of the TEA concentration, H, concentration, temperature, and pressure of P-1/P-E on the yield of the polymer obtained was investigated. The effects of these factors on the glass transition temperature (T,,) and ethylene content of the polymer were studied. The content of ethylene in EPM was determined using the FTIR technique. The molar ratio of Al : MPT : Ti = 355: 107: 1 gave a polymer with an ethylene content of about 32%. However, a ratio lower than AL : MPT : Ti = 355 : 107 : I did not give a good elastomeric polymer. The highest productivity of the catalyst was obtained at a molar ratio of AL : MPT : Ti = 355: 107: 1. Increasing the temperature from 45 to 70degreesC caused a slight increase of Et % content and a decrease of the T-g of the copolymer obtained, while the highest productivity of the catalyst was obtained at 55degreesC with good elastomeric properties using an AL : MPT : Ti = 497 : 107 : 1 molar ratio. Increasing the pressure of propylene from 1.5 to 2.5 atm caused a sharp decrease in the T, and ethylene content of the polymer. When the ethylene content in the copolymer was increased, the T-g value had a tendency to be closer to the polyethylene T-g.