Gornomariysky District (; ; ) is an administrative and municipal district (raion), one of the fourteen in the Mari El Republic, Russia. It is located in the west of the republic and is the only district on the right bank of the Volga River. It borders with Yurinsky District in the north, Kilemarsky District and the Chuvash Republic in the south, and with Nizhny Novgorod Oblast in the west. The area of the district is . Its administrative center is the town of Kozmodemyansk (which is not administratively a part of the district). As of the 2010 Census, the total population of the district was 25,869.