LTI was attempted to modify the microstructure of poly (L-lactic acid) (PLLA) and to improve its mechanical properties in this study. Bending modulus, strength and fracture toughness of PLLA/LTI were evaluated, and compared to those of the base PLLA to assess the effectiveness of LTI blending. Effect of LTI addition on fracture micromechanism was also investigated by observing and comparing the fracture surfaces of PLLA/ LTI and PLLA using a field emission scanning electron microscope (FE-SEM). Experimental results showed that the bending properties such as the bending modulus and the strength are effectively improved due to polymerization of PLLA molecules by LTI blending. The fracture toughness value was also improved due to increase of ductile deformation, i.e., energy dissipation in the crack-tip region.