The effect of α-cyclodextrin (α-CD) on the crystallization behavior of poly(3-hydroxybutyrate) (PHB) was investigated with polarized optical microscopy, differential scanning calorimetry, and wide-angle X-ray diffraction. We found that the addition of α-CD can greatly accelerate the crystallization of PHB and that α-CD has a potential not only to enhance the nucleation but also to accelerate the crystallization of PHB. Compared to a conventional nucleation agent, such as talc, α-CD is a natural product and has many advantages because it is environmentally friendly and safe to humans. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3461–3469, 2004