Avian influenza remains a threat to human wellbeing. Hypochlorite derivatives are commonly used as disinfectants to prevent the spread of the disease. The World Health Organization (WHO) has listed chlorine dioxide (ClOn 2) as an A1-level, safe, and efficient disinfectant. In this study, we tested the efficacy of ClOn 2, in aqueous solution and gas forms, against avian influenza A (H7N9) virus. The virus suspension was mixed with ClOn 2 aqueous solutions of various concentrations and for various time intervals. Aliquots of the mixture were then serially diluted, and the 50% tissue culture infective dose (TCIDn 50) was measured with a hemagglutination test on MDCK cells. ClOn 2 gas produced from generators was introduced in a chamber containing the virus suspension in a Petri dish. The infective activity of the surviving virus was measured by the hemagglutination test. An aqueous solution of ClOn 2 at 126 μg/mL for 15 s was effective given that no surviving virus was detected with the hemagglutination test. ClOn 2 gas at >5 μL/L sustained for 1 h inactivated the virus effectively, while at 2.5 μL/L for 1 h, it only partially inactivated the virus. ClO n 2 as gas or aqueous solution at a certain concentration is effective in inactivating the H7N9 virus, and can be applied for the decontamination and disinfection of environments.n “,”Avian influenza remains a threat to human wellbeing. Hypochlorite derivatives are commonly used as disinfectants to prevent the spread of the disease. The World Health Organization (WHO) has listed chlorine dioxide (ClOn 2) as an A1-level, safe, and efficient disinfectant. In this study, we tested the efficacy of ClOn 2, in aqueous solution and gas forms, against avian influenza A (H7N9) virus. The virus suspension was mixed with ClOn 2 aqueous solutions of various concentrations and for various time intervals. Aliquots of the mixture were then serially diluted, and the 50% tissue culture infective dose (TCIDn 50) was measured with a hemagglutination test on MDCK cells. ClOn 2 gas produced from generators was introduced in a chamber containing the virus suspension in a Petri dish. The infective activity of the surviving virus was measured by the hemagglutination test. An aqueous solution of ClOn 2 at 126 μg/mL for 15 s was effective given that no surviving virus was detected with the hemagglutination test. ClOn 2 gas at >5 μL/L sustained for 1 h inactivated the virus effectively, while at 2.5 μL/L for 1 h, it only partially inactivated the virus. ClO n 2 as gas or aqueous solution at a certain concentration is effective in inactivating the H7N9 virus, and can be applied for the decontamination and disinfection of environments.n