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Magnesium chloride supported vanadium/titanium bimetallic Ziegler-Natta catalysts with di- i-butyl phthalate as internal donor for copolymerization of ethylene and propylene were prepared. The effects of reaction temperature, ethylene/propylene molar ratio, aluminium/vanadium (Al/V) molar ratio and titanium/vanadium molar ratio on the catalytic activity were investigated. The molecular weight, molecular weight distribution, sequence composition and crystallinity of the products were measured by gel permeation chromatography, C-NMR and differential scanning calorimetry analysis, respectively. In comparison to the vanadium and titanium catalysts, the bimetallic catalyst showed higher catalytic activity and better copolymerization performance. The obtained ethylene/propylene copolymers have high molecular weight (10), broad molecular weight distribution, high propylene content with random or short blocked sequence structures ( r r = 1.919), low melting temperatures and low crystallinities ( X < 20%). [ABSTRACT FROM AUTHOR]