Poly(lactic acid) (PLA) is a biodegradable polymer which can be obtained from completely renewable sources such as corn, wheat and rice; hence, it reduces the degree of dependence on petroleum resources. Despite its numerous advantages such as high strength and stiffness its low toughness and brittleness significantly impede its applications; therefore, toughening is required. Poly(butylene adipate-co-terephthalate) (PBATs) and thermoplastic polyurethane (TPU) are good candidates to toughen PLA [1]. PLA/PBAT blends show immiscible behaviour while PLA/TPU blends exhibit partially miscible behaviour [2]. Polyhedral oligomeric silsesquioxanes (POSSs) are nano-particles that create molecular reinforcement and can improve the compatibility between blends. Octaisobutyl-POSSs (O-POSSs) are POSS types that contain eight isobutyl groups [3]. The objective of this study is to compare thermal and thermo-mechanical properties of immiscible PLA/PBAT and partially miscible PLA/TPU blends in the presence of O-POSS. Melt-blending process is used for the preparation of blends. The results indicated that O-POSS positively affected the properties of partially miscible PLA/TPU blends, whereas negatively affected the properties of PLA/PBAT immiscible blends. Acknowledgement: This study is financially supported by TUBITAK (Grant Number: 115M576) References [1] Zhao F., Huang H.X., Zhang S.D., J. Appl. Polym. Sci., 2015 (42511), 1-9. [2] Dogan Kemaloglu S., Reyes E. A., Rastogi S., Ozkoc G., J. Appl. Polym. Sci., 2014(40251), 1-10. [3] Li G., Wang L., Ni H., C. U. Pittman, Journ.of Inorg.and Organomet. Polym., 2001(11-3), 123-54.