The aim of this study was to understand the effect of molding temperature on fracture toughness and microstructure of PLA. The fracture toughness( $K_{IC}$) was measured using single-edge-notch bend(SENB) specimens molded at various molding temperatures. The microstructure around a crack tip of PLA was also observed on a polarizing microscope under the cross polarization. The $K_{IC}$ of PLA decreased with increasing molding temperature because spherulite formation at high molding temperatures suppressed craze formation which is one of the toughening mechanism of thermoplastic materials.s.