Teprenone (Tp) is a widely used pharmaceutically active ingredient in terpene anti-ulcer agents. We investigated Tp and cyclodextrin (CD) complexes for the objective of forming stable Tp powders. Tp was combined with each CD at a molar ratio of 1:2, kneaded together while adding an appropriate amount of water, then dried under reduced pressure and lightly milled into a powder to produce a kneaded mixture (KM). Powder X-ray diffraction of KM containing Tp and beta- and gamma-CD revealed new diffraction peaks. On infrared spectroscopy, the peak near 1718 cm(-1) corresponding to the carbonyl group of Tp had shifted to around 1701 cm(-1). Solid-state NMR spectroscopy showed signs of inhibited molecular mobility of Tp, which is liquid at room temperature, confirming that Tp had formed complexes with beta- and gamma-CD. Photostability analysis of Tp showed improved stability in the order of gamma-CD > beta-CD >> alpha-CD. (C) 2009 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.