The crystal structure of the alpha-form of poly(L-lactide) was analyzed by the linked-atom least-squares refinements for the X-ray fiber diffraction data. The space group was orthorhombic P2(1)2(1)2(1), and the unit cell contained the antiparallel two chains. The chain conformation was the 2-fold s(15*2/7) helix distorted periodically from the regular s(3*10/7) helix. The ester groups were deformed from the planar trans conformation. Potential energy calculations suggested that the periodic chain distortion resulted from the impartial stress distribution due to the interchain interactions.