The present invention provides an exhaust gas treating method by which exhaust gas is passed through a catalyst layer at an areal velocity of 100 to 5000 m.sup.3 /m.sup.2 .multidot.hr to selectively produce carbon monoxide from particulates contained in the exhaust gas, so that nitrogen oxides contained in the exhaust gas are removed by the carbon monoxide thus produced. The exhaust gas treating method of the present invention can readily and securely remove particulates and nitrogen oxides contained in exhaust gas, i.e., two primary causes of air pollution, by merely passing the exhaust gas through a catalyst layer at a specific areal velocity.