This study was mainly to observe the anti-allergic effect of Fructus cnidii ethanol extract. Three methods were chose to observe the anti-allergic effect of Fructus cnidii including rat Passive Cutaneous Anaphylaxis (PCA) tests, rat skull periosteum mast cell degranulation tests, and histamine released factors in rat peritoneal mast cells sensitized mast cells with vitro techniques. The PCA inhibition ratio, the mast cell degranulation ratio and relevant inhibition ratio of drugs, histamine release ratio and relevant inhibition ratio of drugs were all the main indicators needed to dectet. Results showed that Fructus cnidii ethanol extracts could significantly inhibit the PCA reaction in rats, mast cell degranulation in rat skull periosteum as well as the release ratio of histamine. At last, we could come to the conclusion that Fructus cnidii ethanol extract has an obvious anti-type I hypersensitivity effect.