OBJECTIVE: Zingiber cassumunar has been used as a traditional medicine in Thailand and it is known to have anti-allergic activities. The precise effect of Z. cassumunar, however, remains unknown. Our aim was to investigate the anti-allergic substances from Z. cassumunar. METHOD: TLC-guided fraction led to the isolation of main components [(E)-4-(3',4'-dimethoxyphenyl)but-3-en-1ol (compound D) and (E)-1-(3',4'-dimethoxyphenyl)but-1,3-en-diene (DMPBD)] and cis-3-(3',4'-dimethoxyphenyl)-4-[(E)-3',4'-dimethoxystyrl] cyclohex-1-ene (compound B) from Z. cassumunar extracts. To investigate the anti-allergic activities of Z. cassumunar and its component, rat basophilic leukemia (RBL-2H3) cells were sensitized with dinitrophenyl (DNP)-specific IgE overnight. Then cells were incubated with or without test compounds for 10 min and challenged with dinitrophenyl-albumin (DNP-BSA) for 20 min to induce beta-hexosaminidase release as a marker of degranulation. In addition, the effects of Z. cassumunar extracts and isolated constituents on A23187 and PMA-induced release of TNF-α were also examined. RESULTS: DMPBD highly inhibited histamine release with an IC50 value (mean±SE) of 43.34±4.95 µg/ml, followed by compound D (IC50= 87.73±11.78 µg/ml) and crude extracts of (IC50=135.20±11.19 µg/ml) (p≤0.05). Crude Z. cassumunar extract (100µg/ml), DMPBD (100 µg/ml), compound B (100 µg/ml) and compound D (100 µg/ml) inhibited antigen stimulated TNF-α release by 95.00, 56.51, 40.18 and 24.20%, respectively (p≤0.05). CONCLUSION: Our results show that DMPBD, compound D and compound B are responsible for anti-allergic effect of Z. cassumunar. The findings support the traditional use of the plant for treatment of allergy-related diseases.