Ethylene-octene random copolymer (EOC) is one of the most commonly employed elastomers for PP, and as such its rubber toughening efficiency has been extensively studied. However, most existing studies employ EOC containing an octene comonomer of about 8 mol %. Therefore, in this study, we investigated the effect of EOC octene comonomer content on the morphology and thermal and mechanical properties of PP-ethylene random copolymer (PP-CP)/EOC (80/20 wt %/wt %) blends. It was clearly shown that the properties of the blends are significantly affected by the octene content. The rubber particle size of the blends decreased as the octene content in the EOC was increased, which was a consequence of the reduced interfacial tension between PP-CP and EOC. Impact strength of the blends as a function of octene content displayed a brittle-ductile transition. The tensile yield strength and modulus of the PP-CP/EOC blends were decreased by addition of EOC, owing to incorporation of the soft EOC into the hard PP-CP. The tensile yield strength and modulus of PP-CP/EOC blends decreased monotonically with the octene content in the EOC. The melting temperature as well as the crystallinity of the PP-CP phase were not affected significantly by the addition of EOC whereas a notable shift in melting and crystallization temperatures was observed for the EOC phase. (c) 2006 Wiley Periodicals, Inc.