Nikolayevsky District () is an administrative and municipal district (raion), one of the twenty-one in Ulyanovsk Oblast, Russia. It is located in the southwest of the oblast. The area of the district is . Its administrative center is the urban locality (a work settlement) of Nikolayevka. Population: 27,211 (2010 Census); The population of Nikolayevka accounts for 23.5% of the district's total population.