Purpose: To investigate the effects of cyclodextrin (CyD) derivatives on crystallization and solution-mediated polymorphic transition of indomethacin in aqueous solution.Methods: Indomethacin crystals were obtained from aqueous solution in the absence and presence of CyDs at various concentrations in a 50 mL beaker at room temperature.Results:Indomethacin was crystallized into Form Ⅴ crystals from aqueous solutions, whereas 2,6-di-O-methyl-β-cyclodextrin (DM-β-CyD) markedly inhibited the crystallization of indomethacin, giving an amorphous form of the drug and keeping the amorphous state for at least 5 days at 4 ℃C in aqueous solution.No inhibition was observed with other CyDs such as α-, β-and γ-CyDs, 2-hydroxypropyl-α-,-β-, and-γ-CyDs (HP-CyDs) and 2,6-di-O-methyl-α-CyD (DM-α-CyD).Conclusion: The results suggested that the complexation with DM-β-CyD is a valuable tool for the preparation of an amorphous form of indomethacin that occurs at an early stage of crystallization according to "Ostwalds Rule of Stages".