An apparatus for determining an abnormality of a control valve is applied to an internal combustion engine having a first supercharger, a second supercharger, a first control valve, and a second control valve. The apparatus includes an electronic control unit to obtain two supercharging-pressure-corresponding-values before and after an opening degree of the first control valve is changed during a period in which the engine is operated in a specific operating state under which the first supercharger supercharges the engine more efficiently than the second supercharger, and to determine whether or not the second control valve is abnormal based on the two values with respect to the change of the opening degree of the first control valve.