Olefin block copolymers (OBC) is a novel thermoplastic elastomer with excellent properties. However, the insufficiency in mechanical strength limits its application. Polylactic acid (PLA) is a biodegradable and renewable material with high strength and modulus. Hence by blending PLA with OBC can not only improve the mechanical properties of OBC but also reduce the consumption of oil resources. In this work, two kinds of PLA, poly(L-lactide) (PLLA) and sc-PLA powder, which is the stereocomplex of PLLA and its optical isomer poly(D-lactide) (PDLA), were used to enhance the property of OBC and ethylene-methyl acrylate-glycidyl methacrylate (EGMA) was used as a compatibilizer. It is found that as the PLLA contents vary form 5%wt to 30%wt, the tensile strength of OBC/PLLA composites will increase continuously and the elongation at break can be well preserved at the same time. However, the introduction of the sc-PLA have a different influence on the mechanical properties of OBC. With the variation of sc-PLA content, the tensile strength of the OBC/sc-PLA composites increase apparently at 10%wt and then remain unchanged. Meanwhile, the elongation at break decreased appreciably with the sc-PLA content. This can be attributed to the poor dispersion of sc-PLA particles at high loading content.