Objective: To better understand the antagonistic effect of Xiao Long Tong Bi (XLTB), a Chinese herb medicine, on α1-adrenoceptor (α1-AR). Methods: (1) Radio ligand binding assay . Specific　125I-BE2254(2-β(4-hdroxyphenyl)-ethyl amino-methyl-tetralone) binding was measured by incubating membrane of canine cerebral cortex with a single concentration of　125I-BE2254 in the presence of 15 concentrations of XLTB. Half-effectual concentration of inhibition (IC50) and Hill coefficients (nH) were determined by Hill plots. (2) Contractile responses of rat prostate strip in vitro were determined. pKB values for XLTB in competitively inhibiting NE-stimulated contraction of tissues were measured by the method of Ainlakshana. Results: XLTB competitively inhibited binding of　125I-BE2254 to α1-AR in a concentration -dependent manner. IC50 values for XLTB in canine cerebral cortex were (34.0±6.0)　g*L－1, the Hill efficiency value (0.7±0.1) was significantly decreased from unity. Contractile studies showed that XLTB competitively antagonized the NE concentration-response curve with pKB values of (37.0±11.0) g*L－1 or (30.0±8.0) g*L－1 when XLTB concentration was 70 g*L－1 or 170 g*L－1, respectively. The pKB values for XLTB in antagonizing NE-induced contraction of tissues were showed to fit in well with the IC50 values on rat prostate. Conclusion: These results suggest that XLTB appears to be a competitive antagonist for α1-AR.