Abstract: Poly(lactic acid) (PLA)/poly(butyleneadipate-co-terephthalate) (PBAT)/polyhedral oligomeric silsesquioxane (POSS) composites and their foams were prepared by a melt-mixing method and a supercritical CO2 solid state foaming method, respectively. Thermal behavior, rheological property, and foaming behavior of the composites were studied. The results confirmed the plasticization effect of POSS particles on the composites. The rheological results indicated that melt elasticity of the composites was improved with the addition of POSS. As a result, cellular structure of the composites foams was enhanced. Cell density and foaming expansion ratio of the composite foams increased with an increase of POSS content. The composite foams achieved a cell density of 8.25×107 cell/cm3 and an expansion ratio of 13 at the POSS content of 7 phr. POSS was found to have a positive effort on controlling the cellular structure of the composite foams.