OBJECTlVE To elucidate the sensitization mechanism of baicalin in guinea pigs. METHODS Baicalin antigens were prepared by activated ester method. A guinea pig model of allergic shock induced by the coupling was established. Passive cutaneous anaphylaxis ( PCA) was used to ana-lyze the regularity of the specific antibody. The lgG antibodies of baicalin in serum among 19 sensitized guinea pigs were determined by ELlSA. RESULTS UV scanning spectrum couplings occurred between baicalin and protein ( bovine serum albumin and human serum albumin) . The conjugation ratio was 9∶1 and 5∶1, respectively. The guinea pig model of allergic shock was successfully established and suggested that the antigen induced a typical immediate hypersensitivity response. The antibody could be determined on the 19th day and reached the maximum on the 31st day and then degraded gradually. Both specific lgE and lgG existed in the sensitized serum, but there was no correlation between lgG and lgE. The pos-itive rate of specific lgG antibody to baicalin was 84%. The degranulation rate of peritoneal mast cells was (72.6±11.4)%and higher than that incubated with plasma from control (26.8±6.9)%(P<0.05). lsolated ileum from sensitized guinea pigs contracted conspicuously after being challenged by baicalin-human serum albumin. CONCLUSlON Baicalin can induce allergic reaction in guinea pigs and the reaction is correlated with lgE and lgG production.