Abstract: An air-fuel ratio control apparatus for an internal combustion engine has a fuel injection valve for supplying fuel to the engine, a catalytic converter disposed in an exhaust passage of the engine, and an O.sub.2 -sensor for detecting the air-fuel ratio. Before the temperature of the catalytic converter increases to a temperature at which the catalyst is activated, a quantity of unburned fuel present in the exhaust gas is increased by increasing a fuel injection duration within an open intake valve period to a duration Longer than a fuel injection duration within the open intake valve period after activation of the catalytic device.