An exhaust gas purification system for a hybrid vehicle which has, as sources of power, an internal combustion engine performing lean burn operation and an electric motor , and which includes: a generator for generating electricity by power outputted from said internal combustion engine ; a battery that is charged by electric power generated by said generator , and supplies the electric power to said electric motor ; and a control unit that configured to control an operating state of said internal combustion engine and a driving state of said electric motor ; said exhaust gas purification system comprising: an NOx storage reduction catalyst that is arranged in an exhaust passage of said internal combustion engine ; an NOx reduction execution unit configured to carry out NOx reduction processing to reduce NOx stored in said NOx storage reduction catalyst by supplying fuel as a reducing agent to said NOx storage reduction catalyst when a predetermined NOx reduction execution condition is satisfied; and an SOC obtaining unit configured to obtain a state of charge of said battery ; wherein said control unit controls said generator to generate electricity by controlling the operating state of said internal combustion engine so that the state of charge of said battery obtained by said SOC obtaining unit is maintained within a predetermined target SOC range; said control unit performs predetermined power source control, in which an engine rotation speed of said internal combustion engine is made to decrease, or an operation of said internal combustion engine is made to stop, and said electric motor is controlled so as to compensate for required torque, in accompany with the execution of said NOx reduction processing by said NOx reduction execution unit ; characterised in that during a period of execution of said predetermined power source control, said control unit decreases a lower limit value of said predetermined target SOC range from a higher predetermined value C1 to a lower predetermined value C1' smaller than C1; and after the period of execution of said predetermined power source control, said control unit increases the lower limit value of said predetermined target SOC range from the lower predetermined value C1' to the higher predetermined value C1. an NOx storage reduction catalyst that is arranged in an exhaust passage of said internal combustion engine ; an NOx reduction execution unit configured to carry out NOx reduction processing to reduce NOx stored in said NOx storage reduction catalyst by supplying fuel as a reducing agent to said NOx storage reduction catalyst when a predetermined NOx reduction execution condition is satisfied; and an SOC obtaining unit configured to obtain a state of charge of said battery ; wherein said control unit controls said generator to generate electricity by controlling the operating state of said internal combustion engine so that the state of charge of said battery obtained by said SOC obtaining unit is maintained within a predetermined target SOC range; said control unit performs predetermined power source control, in which an engine rotation speed of said internal combustion engine is made to decrease, or an operation of said internal combustion engine is made to stop, and said electric motor is controlled so as to compensate for required torque, in accompany with the execution of said NOx reduction processing by said NOx reduction execution unit ; characterised in that during a period of execution of said predetermined power source control, said control unit decreases a lower limit value of said predetermined target SOC range from a higher predetermined value C1 to a lower predetermined value C1' smaller than C1; and <EOS>