Polybutadienes (PBs) are found to form inclusion complexes with cyclodextrins (CDs) stereoselectively to give crystalline compounds in bulk. These complexes have been isolated and characterized by means of H-1 NMR and C-13 CP/MAS NMR spectroscopy, and X-ray diffraction. Although alpha-CD did not form inclusion complexes with any kinds of PBs in aqueous solutions, alpha-CD did form inclusion complexes with PBs having 1,4-cis- and 1,4-trans-butadiene units in bulk by heating at 100 degrees C. On the other hand, PB having 79% of a 1,2-structure did not form inclusion complexes with alpha-CD. The yield of the inclusion complexes increases with an increase in the content of the 1,4-cis-structure of PB and decreases with the molecular weights of the PBs.