A control system for an internal combustion engine having a throttle valve disposed in an intake passage of said engine, comprising: rotational speed detecting means for detecting a rotational speed of said engine; intake pressure detecting means for detecting an intake pressure of said engine; wide-open intake air amount calculating means for calculating a wide-open intake air amount (GAWOT) according to the engine rotational speed, the wide-open intake air amount (GAWOT) being an intake air amount corresponding to a state where said throttle valve is fully opened; theoretical intake air amount calculating means for calculating a theoretical intake air amount (GATHTMP) according to the wide-open intake air amount (GAWOT) and the intake pressure, the theoretical intake air amount (GATHTMP) being an intake air amount corresponding to a state where no exhaust gas of said engine is recirculated to a combustion chamber of said engine; estimated intake air amount calculating means for calculating an estimated intake air amount (HGAIR, GACMDMID) which is an estimated value of an actual intake air amount of said engine; exhaust gas recirculation ratio calculating means for calculating an exhaust gas recirculation ratio (REGRTTMP) using the theoretical intake air amount (GATHTMP) and the estimated intake air amount (HGAIR, GACMDMID); torque detecting means for detecting an output torque (TRQDET) of said engine; and control means for controlling said engine using the estimated intake air amount (HGAIR, GACMDMID), wherein said estimated intake air amount calculating means calculates the estimated intake air amount (HGAIR, GACMDMID) using the detected output torque (TRQDET) and the exhaust gas recirculation ratio (REGRTTMP). rotational speed detecting means for detecting a rotational speed of said engine; intake pressure detecting means for detecting an intake pressure of said engine; wide-open intake air amount calculating means for calculating a wide-open intake air amount (GAWOT) according to the engine rotational speed, the wide-open intake air amount (GAWOT) being an intake air amount corresponding to a state where said throttle valve is fully opened; theoretical intake air amount calculating means for calculating a theoretical intake air amount (GATHTMP) according to the wide-open intake air amount (GAWOT) and the intake pressure, the theoretical intake air amount (GATHTMP) being an intake air amount corresponding to a state where no exhaust gas of said engine is recirculated to a combustion chamber of said engine; estimated intake air amount calculating means for calculating an estimated intake air amount (HGAIR, GACMDMID) which is an estimated value of an actual intake air amount of said engine; exhaust gas recirculation ratio calculating means for calculating an exhaust gas recirculation ratio (REGRTTMP) using the theoretical intake air amount (GATHTMP) and the estimated intake air amount (HGAIR, GACMDMID); torque detecting means for detecting an output torque (TRQDET) of said engine; and control means for controlling said engine using the estimated intake air amount (HGAIR, GACMDMID), wherein said estimated intake air amount calculating means calculates the estimated intake air amount (HGAIR, GACMDMID) using the detected output torque (TRQDET) and the exhaust gas recirculation ratio (REGRTTMP).