Poly(butylene succinate) (PBS) is a worthy biodegradable thermoplastic polyester for blending along with other biopolymers, especially with poly (lactic acid) (PLA), to overcome its inadequacies in mechanical and thermal characteristics. Since binary blends of PLA and PBS showed that they are incompatible, compatibilization is required. In this work, multi‐epoxide polyhedral oligomeric silsesquioxane (Glycidyl POSS) was added to PLA and PBS using the melt blending method to make them compatible. The blends were prepared at different weight ratios having different amounts of compatibilizer. SEM analysis showed that the Glycidyl POSS impacted the interfacial adhesion and other properties of PLA and PBS blends. Noticeable improvements in mechanical properties were revealed by tensile and impact test results. Tensile strength and Young's modulus were improved when epoxy‐POSS was added up to 1 and 3 wt% into ternary blends, but further increasing POSS concentrations resulted in lower values. FTIR analysis showed a strong interaction between the epoxide group of POSS and the end groups of PBS or PLA. The thermal properties of samples were analyzed using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. The shifts in glass transition temperatures of the PLA phase towards lower values appeared in DSC, confirming the enhanced compatibility of PLA and PBS. Also, the reinforcing ability of the POSS inorganic core structure impacted the thermal stability of the blends.