The formation behavior of inclusion complexes between gamma-cyclodextrin (gamma-CD) and poly(methacrylic acid)s (PMAAs) of different stereoregularities in water was examined by analyzing the precipitate formed by mixing gamma-CD with each PMAA in water. When syndiotactic (st-) PMAA was used as a guest, a much larger amount of precipitate was formed as compared to isotactic (it-) and atactic (at-) PMAAs. X-ray diffraction, FT-IR, and H-1 NMR measurements of the precipitate indicated that gamma-CD effectively formed an inclusion complex with st-PMAA. Upon increasing the syndiotacticity of PMAA, the yield and the coverage ratio of the resulting inclusion complexes increased, suggesting that gamma-CD more effectively includes PMAA of a higher syndiotacticity. This is the first example of selective inclusion complex formation between CDs and a syndiotactic polymer. By adding gamma-CD into a mixture of st- and at-PMAAs, the selective extraction of st-PMAA was successfully achieved through gamma-CD st-PMAA inclusion complex formation. Additionally, the formation of a gamma-CD st-PMAA inclusion complex in the aqueous solution was confirmed by H-1 NMR, NOESY, and dynamic light scattering measurements. By changing the pH of the solution, the formation and dissociation of the gamma-CD st-PMAA inclusion complex were reversibly controlled. This pH-controllable inclusion complex can be useful as a novel building block for pH-responsive materials.