Two highly conserved 15 base sequences of influenza A virus genome were identified by CONSERV software, which can detect contiguous conserved sequences of biological sequences. Antiviral effect of phosphorothioate oligonucleotide that target these conserved sequences was evaluated by plaque formation assay and cell viability assay. Pre-treatment of cells with anti-PB2 (RNA polymerase subunit) reduced the size of plaques in a sequence dependent manner. Post-treatment of cells with anti-PB2 phosphorothioate oligonucleotide inhibited the virus-induced cytotoxicity.