AbstractInfluenza A virus (IAV) causes great morbidity and mortality worldwide every year. However, there are only a limited number of drugs clinically available against IAV infection. Further, emergence of drug‐resistant strains can render those drugs ineffective. Thus there is an unmet medical need to develop new anti‐influenza agents. In this study, we show that punicalagin from plants possesses strong anti‐influenza activity with a low micromolar IC50 value in tissue culture. Using a battery of bioassays such as single‐cycle replication assay, neuraminidase (NA) inhibition assay, and virus yield reduction assay, we demonstrate that the primary mechanism of action (MOA) of punicalagin is the NA‐mediated viral release. Moreover, punicalagin can inhibit replication of different strains of influenza A and B viruses, including oseltamivir‐resistant virus (NA/H274Y), indicating that punicalagin is a broad spectrum antiviral against both IAV and IBV. Further, although punicalagin targets NA like oseltamivir, it has a different MOA. These results suggest that punicalagin is an influenza NA inhibitor that may be further developed as a novel antiviral against influenza viruses.