The present invention relates to a composition having antiviral activity for prophylaxis or treatment of flavivirus infection or a disease resulting therefrom in humans or animals, characterised in that said composition consisting of baicalein, or analogues, or derivatives thereof. The composition may further comprise a pharmaceutically acceptable carrier. The antiviral activity may include inhibition of virus attachment to host cells, inhibition of intracellular virus replication and direct virucidal activity. The flavivirus may comprise dengue virus type-1, dengue virus type-2, dengue virus type-3, dengue virus type-4 and Japanese encephalitis virus.