As for the crystal structure of poly(3-hydroxybutyrate) (PHB) α-form, the methyl group was said to locate at an abnormally short distance from the oxygen atom of C═O unit, resulting in the formation of CH3···O═C hydrogen bond. This idea was proposed on the basis of infrared spectra detecting a band of antisymmetric methyl C–H stretching mode [νas(CH3)] at anomalously high frequency position and the too short CH3···O═C interatomic distances calculated from the atomic coordinates derived from the previously reported X-ray structure analysis. However, the crystal structure analyzed by the X-ray method, even the C and O atomic positions, has not yet been established confirmatively because of the appreciably small number of the observed X-ray diffraction spots. We have reinvestigated the crystal structure of PHB α-form by collecting the observed X-ray diffraction spots of about twice larger total number than before, and confirmed the positions of the C, O and H atoms in the unit cell at enough high accuracy. T...