We investigated the structural anisotropy of poly(lactic acid) (PLA) film samples by polarizationsensitive(PS) terahertz time-domain spectroscopy (THz-TDS). The dielectric function of the PLA filmbecomes more anisotropic with the sample's increased draw ratio. This behavior is explained by theclassical Lorentz oscillator model that takes into account the orientation of PLA chains along thestretching direction. For further understanding of structural anisotropy in PLA, we performed twodimensional(2D) wide-angle X-ray scattering (WAXS) experiments and found that anisotropy isstrongly correlated to the orientation of the crystalline PLA chains. Our results suggest that PS THz-TDS is more suitable for examining the anisotropy of amorphous PLA chains.