An exhaust gas purification system for an internal combustion engine, comprising: an NOx storage reduction catalyst provided in an exhaust passage of an internal combustion engine; EGR means for introducing a portion of exhaust gas flowing in an exhaust system (6, 7) of the internal combustion engine into an intake system (4, 5) of the internal combustion engine as EGR gas; and NOx reduction means for decreasing the air-fuel ratio of ambient atmosphere around said NOx storage reduction catalyst to a target air-fuel ratio by decreasing the air-fuel ratio of exhaust gas discharged from the internal combustion engine, thereby reducing NOx stored in said NOx storage reduction catalyst, wherein when NOx stored in said NOx storage reduction catalyst is to be reduced, if the temperature of said NOx storage reduction catalyst is equal to or higher than a specific temperature, said NOx reduction means decreases the air-fuel ratio of ambient atmosphere around said NOx storage reduction catalyst to said target air-fuel ratio while making the quantity of the EGR gas in a cylinder larger than a quantity that maximizes the amount of generated smoke and achieving low temperature combustion in the internal combustion engine, and if the temperature of said NOx storage reduction catalyst is lower than said specific temperature, said NOx reduction means decreases the air-fuel ratio of ambient atmosphere around said NOx storage reduction catalyst to said target air-fuel ratio while decreasing the quantity of the EGR gas in the cylinder so that the amount of generated smoke is kept within an allowable range, said exhaust gas purification system being characterized in that said specific temperature is defined as a threshold value at which it can be concluded that even if the temperature of exhaust gas decreases due to said low temperature combustion achieved in the internal combustion engine, the temperature of said NOx storage reduction catalyst will not become so low that the NOx reduction ratio becomes unduly low. an NOx storage reduction catalyst provided in an exhaust passage of an internal combustion engine; EGR means for introducing a portion of exhaust gas flowing in an exhaust system (6, 7) of the internal combustion engine into an intake system (4, 5) of the internal combustion engine as EGR gas; and NOx reduction means for decreasing the air-fuel ratio of ambient atmosphere around said NOx storage reduction catalyst to a target air-fuel ratio by decreasing the air-fuel ratio of exhaust gas discharged from the internal combustion engine, thereby reducing NOx stored in said NOx storage reduction catalyst, wherein when NOx stored in said NOx storage reduction catalyst is to be reduced, if the temperature of said NOx storage reduction catalyst is equal to or higher than a specific temperature, said NOx reduction means decreases the air-fuel ratio of ambient atmosphere around said NOx storage reduction catalyst to said target air-fuel ratio while making the quantity of the EGR gas in a cylinder larger than a quantity that maximizes the amount of generated smoke and achieving low temperature combustion in the internal combustion engine, and if the temperature of said NOx storage reduction catalyst is lower than said specific temperature, said NOx reduction means decreases the air-fuel ratio of ambient atmosphere around said NOx storage reduction catalyst to said target air-fuel ratio while decreasing the quantity of the EGR gas in the cylinder so that the amount of generated smoke is kept within an allowable range, said exhaust gas purification system being characterized in that said specific temperature is defined as a threshold value at which it can be concluded that even if the temperature of exhaust gas decreases due to said low temperature combustion achieved in the internal combustion engine, the temperature of said NOx storage reduction catalyst will not become so low that the NOx reduction ratio becomes unduly low.