Poly(lactic acid) (PLA), a considerable biopolymer, suffers from the significant brittleness, which is one of its main limitations for industrial use or for biomedical applications. Introducing nanofillers represents a promising way to extend and to improve the performance of a polymer matrix. In this study, a series of octa-armed polyhedral oligomeric silsesquioxanes (POSS-(PLLA)(8)) were developed to introduce amount of poly(L-lactide) (PLLA) arms onto the POSS particles. Then PLLA/POSS-(PLLA)(8) nanocomposites were prepared via solvent casting technique. By combining the PLLA arms onto POSS particles, the interfacial interaction between PLLA and POSS can be significantly improved and the stereocomplexed crystal are formed by heterogeneous nucleating effect of POSS-(PLLA)(8). With the addition of 4 wt% POSS-(PLLA)(8), an unprecedented improvement in elongation at break of the system of 600% is obtained. Simultaneously the Young's modulus is 48% improved and the tensile strength increases 56%. The PLLA/POSS-(PLLA)(8) nanocomposite possessing a high toughness and strength, improved thermal stability, as well as excellent cell attachment, spreading and proliferation is a potential biomaterial for tissue engineering applications.