Oseltamivir is a neuraminidase inhibitor used in the treatment of and prophylaxis of both influenza A and influenza B. Oseltamivir was the first orally active neuraminidase inhibitor commercially developed. It was developed by Gilead Sciences and is currently marketed by Hoffman La Roche under the trade name Tamiflu®.

Oseltamivir is a prodrug, usually administered as oseltamivir phosphate, with the drug being converted heptically to the active metabolite GS4071 in vivo.

Like zanamivir, oseltamivir acts as a transition-state analogue inhibitor of influenza neuraminidase.

On March 1st 2005, the U.K. government announced that it would be stockpiling enough oseltamivir to treat a quarter of the country's population, in preparation for a possible avian flu pandemic.