We investigated the aqueous solubility of paclitaxel using 11 kinds of cyclodextrins (CDs) and the bioactivity of the paclitaxel-CD inclusion complex. 2,6-Dimethyl beta-cyclodextrin was the most effective and its solubility was 2.3 mM in a 0.1 M 2,6-dimethyl beta-cyclodextrin aqueous solution. The inclusion complex of paclitaxel and 2,6-dimethyl beta-cyclodextrin had a 1.23-fold polymerization activity as paclitaxel in a tubulin assay.