An exhaust purification system for an internal combustion engine capable of lean-burn driving comprises: an NSR catalyst disposed in an exhaust passageway; an SCR disposed downstream of the NSR catalyst; a NOx sensor, disposed downstream of the SCR, for producing output in response to NOx concentration; and rich-spike means for causing a rich-spike. When the NOx sensor has produced output indicative of a NOx concentration higher than a given NOx concentration, the system increases the amount of the NOx contained in the exhaust gas discharged during the rich-spike. Under a given high-load condition, the air-fuel ratio is made stoichiometric during the rich-spike caused at a particular timing. Under a given low-load condition, the amount of exhaust gas is increased during the rich-spike.