Abstract: The carbon dioxide adsorbent composition relates to a material that will adsorb carbon dioxide gas from the atmosphere and that is made by the treatment of oil fly ash with ammonium hydroxide. In order to make the carbon dioxide adsorbent, oil fly ash is first mixed with ammonium hydroxide. This mixture is then refluxed and cooled. Additional ammonium hydroxide is added to the cooled mixture of oil fly ash and ammonium hydroxide to form a secondary mixture. This forms an amine-functionalized fly ash composition, which is then filtered from the secondary mixture to be used as a carbon dioxide adsorbent composition. The carbon dioxide adsorbent composition is then dried and may be used as a carbon dioxide adsorbent for gas streams, such as flues and exhaust systems, containing carbon dioxide.