A method for producing a polyvinyl acetal resin is provided which is characterized in that a polyvinyl alcohol and a carbonyl compound are reacted at 40 to 200°C in a liquid containing water and/or an alcohol as solvents in the presence of an acid catalyst including carbon dioxide. By this method, a polyvinyl acetal resin having a halogen element content of 100 ppm or less and an alkali metal element content of 1000 ppm or less can be obtained without particularly performing washing operations. Therefore, a method for producing a polyvinyl acetal resin containing only little impurities such as metal salts and acids is provided.