Mykolaiv Raion () was a raion (district) in Lviv Oblast in western Ukraine. Its administrative center was Mykolaiv. The raion was abolished on 18 July 2020 as part of the administrative reform of Ukraine, which reduced the number of raions of Lviv Oblast to seven. The area of Mykolaiv Raion was merged into Stryi Raion. The last estimate of the raion population was
It was established in 1939.
At the time of disestablishment, the raion consisted of three hromadas: Mykolaiv urban hromada with the administration in Mykolaiv; Rozvadiv rural hromada with the administration in the selo of Rozvadiv; Trostianets rural hromada with the administration in the selo of Trostianets.