Abstract: In the present investigation, horseradish peroxidase (HRP) was used as the marker and polystrene micro-haemaglutination plates was used as the solid carrier. The EIA for thrombin-like enzyme (TLE) partially purified from the Agkistrodon acutus venom was studied with the sandwich ELISA. It was shown that the sandwich ELISA for TLE was a sensitive and specific method. The minimum concentration of TLEthat could be detected was as low as 1～5 ng.ml^-1 with reproducibility. The "s"-type logarithm dose reaction curve of TLE in rat plasma was fitted on FO-3 microcomputer using the logarithm model with four parameters and BASIC program based on nonlfnear least square satisfactorily.