The work aims at the experimental and theoretical determination of the effect of the air addition on the performance of solid propellant Integral Rocket-Ramjet Motors 1RRM's. An experimental investigation was carried out to determine the specific impulse dependence on the air equivalence ratio, using an 80 mm motor with exchangeable external and intermediate nozzles. Air inlets and secondary combustion chamber were kept unchanged. The ducted air by ram effect was simulated in this ground testing by feeding pressurized air into the secondary combustion chamber. The experimental investigation showed that the motor specific impulse was increased by about 85% when the air equivalence ratio was increased from zero to ..bout 0.7.A simple one dimensional mathematical model of a solid propellant IRRM atsteady state is presented. The numerical calculations based onthe presented model showed good agreement with the test results.