Curcuma aromatica is a plant belonging to genus Curcuma of family Zingiberaceae and is widely used as supplements in Japan. Rhizomes of C. aromatica have curcumin as a major yellow pigment and curdione as a main ingredient of essential oils. The affect of C. aromatica on CYP3A4 using 1α,25-(OH)(2)-D(3)-treated Caco-2 clone cells. Caco-2 cells were treated with methanol extract (0.1 mg ml(-1)), its hexane soluble fraction (0.1 mg ml(-1)), curcumin (4 μM) and curdione (20 μM) for 72 hours. Nifedipine was used as a substrate of CYP3A4. Moreover, all of methanol extract, hexane fraction and curdione decreased CYP3A4 protein expression but had no affect on CYP3A4 mRNA expression. These findings suggest that curdione plays an important role in the CYP3A4 inhibitory activity of C. aromatica and curdione might inhibit the activity by accelerating the degradation of CYP3A4.