The present study aims to clarify the inhibitive effect of the compounds from Rheum palmatum L. on the SARS-3CL protease. The SARS-CoV 3CL gene was amplified from RNA of the SARS virus by PCR. The SARS-CoV 3CL protease was purified from a colon bacillus recombinant. Drugs and 3CL protease were incubated together. The inhibition rate and IC(50) were calculated based on absorbance. Components from the Rheum palmatum L. had a high level of anti-SARS-CoV 3CL protease activity. The IC(50) was 13.76 +/- 0.03 microg/mL and the inhibition rate was up to 96%. In conclusion, extracts from Rheum palmatum L. have a high level of inhibitory activity against 3CL protease, suggesting that extracts from Rheum palmatum L. may represent a potential therapeutic for SARS.