Poly(butylene succinate-co-L-lactate) (PBSL)compatibilized poly(L-lactide) (PLLA) polymer blends with two commercial grades of polycarbonate (PC) were investigated. The capillary tests showed that the steady shear viscosity of high molecular weight PC (PC-L) was 10 times higher than that of low molecular weight PC (PC-AD) throughout the shear rate range under investigation. Morphologic examination revealed that the shape of the dispersed PC-L phase in the as-extruded blends was largely spherical, but the PC-AD phase was more like a rod and elongated further during injection molding. Notched Izod impact strength (IS) of the unmodified PLLA/PC-L blend was higher than that of PC-AD blend. The IS of modified ternary blends increased with PBSL content because of enhanced phase interaction indicated from thermal and morphologic analysis. The PBSL modification also enhanced IS more significantly in PLLA/PC-L than in PLLA/PC-AD blends. On the contrary, the heat deflection temperature (HDT) of PLLA/PC-L binary system was much lower than that of PLLA/PC-AD. HDT of PBSL-modified PLLA/PC-AD blends dropped with increasing PBSL content, which is a ductile polymer. Thermal and dynamic mechanical analysis of the ternary blends showed that individual components were immiscible with distinct Tgs for PC and PLLA and distinct Tms for PBSL and PLLA. POLYM. ENG. SCI., 2013. (c) 2012 Society of Plastics Engineers