An object is to provide an exhaust purifying system for an internal combustion engine having an NSR catalyst, which can inhibit emissions from being aggravated by blow-by of NOx. An exhaust purifying system for an internal combustion engine capable of a lean burn operation is provided. The exhaust purifying system includes: an NSR catalyst disposed in an exhaust passage of the internal combustion engine; an SCR disposed downstream of the NSR catalyst; a NOx sensor disposed downstream of the SCR, the NOx sensor producing an output according to an NH3 concentration; and rich spike means for performing a rich spike. The rich spike means starts the rich spike at a predetermined timing during a lean burn operation and terminates the rich spike at a timing when the NOx sensor issues a predetermined output characteristic indicative of a rise in the NH3 concentration.