An exhaust gas purifying system for an internal combustion engine including at least one combustion chamber connected to an intake port through an intake valve. The system comprises a first passage for passing a portion of exhaust gases discharged from the combustion chamber, a second passage for passing air, a fluid passage, at least one fluid injection nozzle having its one end connected to the fluid passage and the other end extending into the intake port toward the combustion chamber, the fluid injection nozzle adapted to open when the intake valve opens, and means responsive to engine operating condition for connecting the fluid passage to the first passage to permit injection of exhaust gases through the fluid injection nozzle into the combustion chamber during acceleration and for connecting the fluid passage to the second passage to permit injection of air through the fluid injection nozzle into the combustion chamber during normal operation or idling.