– Oxocarbazate, also known as CID23631927, is an inhibitor of human cathepsin L. In the cathepsin L inhibition assay, The oxocarbazate caused a time-dependent 17-fold drop in IC50 from 6.9 nM (no preincubation) to 0.4 nM (4-h preincubation). Slowly reversible inhibition was demonstrated in a dilution assay. CID23631927 demonstrate activity in blocking both SARS-CoV (IC50 = 273 nM) and Ebola virus (IC50 = 193 nM) entry into human embryonic. CID 23631927 was a subnanomolar, slow-binding, reversible inhibitor of human cathepsin L that blocked SARS-CoV and Ebola pseudotype virus entry in human cells. Inhibition of cathepsin L thus holds promise for therapeutic intervention for both SARS-CoV and Ebola virus infection.