The Russian occupation of Mykolaiv Oblast is an ongoing military occupation of Ukraine's Mykolaiv Oblast by Russian forces during the Russian invasion of Ukraine as part of the southern Ukraine campaign. The Russian-installed occupation regime was called the "Nikolaev military-civilian administration".

Military occupation, also called belligerent occupation or simply occupation, is the temporary control exerted by a ruling power's military apparatus over a sovereign territory that is outside of the legal boundaries of that ruling power's own sovereign territory. The controlled territory is then known as the occupied territory, with the ruling power being the occupant. Occupation is distinguished from annexation and colonialism on the basis that it is a power structure that the ruling power intends to keep in place only temporarily. In many cases, the occupant may establish a military government to facilitate the administration of the occupied territory, though this is not a necessary precondition for occupation to take place.