Abstract: A gas generating composition which is excellent in a combustion efficiency and a gas output and in which amounts of residues generated are reduced in the combustion is obtained. A gas generating composition comprising (a) 5 to 40% by weight of at least one high polymer selected from the group consisting of a polyacrylic derivative resin, a polyacetal, a urea resin, a melamine resin, a ketone resin and a cellulose-based high polymer, and (b) 60 to 95% by weight of ammonium nitrate or phase-stabilized ammonium nitrate. It is suitable as a gas generating agent for an air bag of automobiles.