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Quinone-methide triterpenes, celastrol (1), pristimerin (2), tingenone (3), and iguesterin (4) were isolated from Triterygium regelii and dihydrocelastrol (5) was synthesized by hydrogenation under palladium catalyst. Isolated quinone-methide triterpenes (1–4) and 5 were evaluated for SARS-CoV 3CL^pro inhibitory activities and showed potent inhibitory activities with IC₅₀ values of 10.3, 5.5, 9.9, and 2.6μM, respectively, whereas the corresponding 5 having phenol moiety was observed in low activity (IC₅₀=21.7μM). As a result, quinone-methide moiety in A-ring and more hydrophobic E-ring assist to exhibit potent activity. Also, all quinone-methide triterpenes 1–4 have proven to be competitive by the kinetic analysis.