In the last decade, the usage of plastics has become very popular in many areas owing to their several advantages. However the solid waste problem creates morality issues due to environmental problems. In order to prevent the pollution problem, biodegradable polymers have been focused by many researches. Recently, poly(lactic acid) (PLA) becomes most widely desired biodegradable polymer due to its good physical properties and being produced from renewable resources with an economical price [1]. Poly(butylene adipate-co-terephatalate) (PBAT) obtained from petrochemical resources is another biodegradable polymer and that can be easily processed without any converse effects on the environment. It can be also used to toughen PLA via melt blending [2]. Polyhedral oligomeric silsesquioxanes (POSS) organic/inorganic hybrid materials are new generation nano-fillers and could provide molecular reinforcement, increased thermal stability and better flame resistance [3]. The aim of this study is to investigate the effects of octaisobutyl-POSS (OPOSS) on the properties of PLA/PBAT blends. The PBAT molecular weight and OPOSS concentration was taken as the experimental parameters. Blends were prepared in a laboratory twin-screw microcompounder. Mechanical, thermal and rheological properties were characterized. The results showed that the high molecular weight of PBAT improved the mechanical properties of blends such as elongation at break and impact strength. Incorporation of OPOSS enhanced the compatibility between PBAT/PLA regardless of PBAT’s molecular weight. In addition, thermal properties were also affected positively. Acknowledgement: This study is financially supported by TUBITAK (Grant Number:115M576) References [1] R. Narayan, K.Schcaf, ASTM Standardization News, (1992), 23-26. [2] J. B. Olivato, M. V. E. Grossmann, F. Yamashita, D. Eiras, L. A. Pessan, Carbohydrate Polymer, 87 (2012), 2614-2618. [3] M. Kodal, H. Sirin, G. Ozkoc, Polym. Comp., 10.1002 , (2015), 264-275.