H5 high pathogenicity avian influenza virus (HPAIV) continues to spread globally, causing several high pathogenicity avian influenza (HPAI) outbreaks in poultry and significant economic losses. Biosecurity measures that prevent the introduction of HPAIV represent a top priority for controlling HPAI outbreaks on poultry farms. Although these measures are crucial for minimizing HPAI introduction, outbreaks of viral infection on poultry farms persist, underscoring the importance of continuously improving biosecurity protocols. Therefore, safe and effective microbicide disinfectants could play an essential role in reducing viral spread by inactivating viral particles on surfaces and in the air. This study assessed the efficacy of gaseous chlorine dioxide (ClO2) against H5 HPAIV under both gaseous ClO2 inactivation setting and in vivo conditions. In the gaseous ClO2 inactivation setting, only low virus titers were recovered (