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Coronavirus disease 2019 (COVID‐19) is caused by SARS‐CoV‐2 and has spread across the globe. SARS‐CoV‐2 is a highly infectious virus with no vaccine or antiviral therapy available to control the pandemic; therefore, it is crucial to understand the mechanisms of viral pathogenesis and the host immune responses to SARS‐CoV‐2. SARS‐CoV‐2 is a new member of the betacoronavirus genus like other closely related viruses including SARS‐CoV and Middle East respiratory syndrome coronavirus (MERS‐CoV). Both SARS‐CoV and MERS‐CoV have caused serious outbreaks and epidemics in the past eighteen years. Here, we report that one of the interferon‐stimulated genes (ISGs), cholesterol 25‐hydroxylase (CH25H), is induced by SARS‐CoV‐2 infection in vitro and in COVID‐19‐infected patients. CH25H converts cholesterol to 25‐hydrocholesterol (25HC) and 25HC shows broad anti‐coronavirus activity by blocking membrane fusion. Furthermore, 25HC inhibits USA‐WA1/2020 SARS‐CoV‐2 infection in lung epithelial cells and viral entry in human lung organoids. Mechanistically, 25HC inhibits viral membrane fusion by activating the ER‐localized acyl‐CoA:cholesterol acyltransferase (ACAT) which leads to the depletion of accessible cholesterol from the plasma membrane. Altogether, our results shed light on a potentially broad antiviral mechanism by 25HC through depleting accessible cholesterol on the plasma membrane to suppress virus–cell fusion. Since 25HC is a natural product with no known toxicity at effective concentrations, it provides a potential therapeutic candidate for COVID‐19 and emerging viral diseases in the future. Synopsis: 25‐Hydroxycholesterol, produced by the interferon‐stimulated protein CH25H, inhibits the entry of SARS‐CoV‐2, SARS‐CoV, and MERS‐CoV. Mechanistically, 25HC activates the ER‐localized enzyme ACAT, whose activity depletes accessible cholesterol on the plasma membrane and restricts viral membrane fusion. An interferon‐stimulated gene, CH25H is induced in SARS‐CoV-2 infection in vitro and in vivo.25HC exhibits broad anti‐coronavirus activity by blocking membrane fusion.25HC activates ACAT to induce internalization of accessible cholesterol on the plasma membrane and restricts viral fusion.25HC inhibits USA‐WA1/2020 SARS‐CoV-2 infection in lung epithelial cells and virus entry in human lung organoids. [ABSTRACT FROM AUTHOR]