COVID-19 pandemic results in record high deaths in many countries . Although a vaccine for SARS-CoV-2 is now available, effective antiviral drugs to treat coronavirus diseases are not available yet . Recently, EGCG, a green tea polyphenol, was reported to inhibit SARS-CoV-2 3CL-protease, however the effect of EGCG on coronavirus replication is unknown . In this report, human coronavirus HCoV-OC43 (beta coronavirus) and HCoV-229E (alpha coronavirus) were used to examine the effect of EGCG on coronavirus . EGCG treatment decreases 3CL-protease activity of HCoV-OC43 and HCoV-229E . Moreover, EGCG treatment decreased HCoV-OC43-induced cytotoxicity . Finally, we found that EGCG treatment decreased the levels of coronavirus RNA and protein in infected cell media . These results indicate that EGCG inhibits coronavirus replication.