Kaempferia parviflora is one of the plants in the Zingiberaceae family, locally known in Thai as kra-chai-dam. In Thai traditional medicine, the decoction of Kaempferia parviflora powder with alcohol has been reported to cure allergy, asthma, impotence, gout, diarrhea, dysentery, peptic ulcer and diabetes. Therefore, the present study aimed to investigate anti-allergic substances from this plant. Bioassay-guided fractionation led to the isolation of seven methoxyflavone derivatives (1-7) from Kaempferia parviflora extract and they were identified on the basis of spectroscopic methods. Among the compounds tested, 5-hydroxy-3,7,3',4'-tetramethoxyflavone (5) possessed the highest anti-allergic activity against antigen-induced beta-hexosaminidase release as a marker of degranulation in RBL-2H3 cells with an IC(50) value of 8.0 microM, followed by 5-hydroxy-7-methoxyflavone (2, IC(50)=20.6 microM) and 5-hydroxy-7,4'-dimethoxyflavone (4, IC(50)=26.0 microM), whereas others showed moderate activities (IC(50)=37.5-66.5 microM). Structure-activity trends of 7-methoxyflavone derivatives on anti-allergic activity can be summarized as follows: (1) substitution with vicinal methoxyl groups at positions 3' and 4' conferred higher activity than only one methoxylation, (2) methoxylation at position 3 reduced activity and (3) methoxylation at position 5 showed higher activity than hydroxylation. Compounds 2, 4 and 5 were also determined for their mechanisms on ionomycin-induced beta-hexosaminidase release. The results indicated that the mechanism on inhibition of cell degranulation of compounds 2 and 5 mainly involve the inhibition of Ca(2+) influx to the cells, whereas that of 4 may be partly due to this inhibition. In regards to the active constituents for anti-allergic activity of Kaempferia parviflora, 5-hydroxy-3,7,3',4'-tetramethoxyflavone (5), 5-hydroxy-7-methoxyflavone (2) and 5-hydroxy-7,4'-dimethoxyflavone (4) are responsible for anti-allergic effect of this plant. The findings support the traditional use of Kaempferia parviflora rhizomes for treatment of allergy and allergy-related diseases.