Viral polymerase-IN-1 hydrochloride, a Gemcitabine derivative, potently inhibits influenza A and B viruses infection with IC 90 values of 11.4-15.9 μM. Viral polymerase-IN-1 hydrochloride is active against SARS-CoV-2 infection. Viral polymerase-IN-1 hydrochloride suppresses influenza virus infection by affecting viral RNA replication/transcription in cells.