Oneşti is a city in Bacău County, Romania.
Administratively, the villages of Slobozia and Borzeşti form part of Oneşti. Borzeşti, site of the Borzeşti Church, was the birthplace of Stephen III of Moldavia.
The city was founded as a village on December 14, 1458, and it is said that was named after prince Stephen the Great's daughter, Oana, its overlord. At the death of the Communist leader Gheorghe Gheorghiu-Dej in March 1965, it was renamed Gheorghe Gheorghiu-Dej but the name was changed back in 1990.
Oneşti is located in the Tazlău-Caşin Depression at an altitude of 175 m.
Saint Nicholas is the patron saint of the city, whose inhabitants are predominantly Romanian Orthodox. St. Nicholas Day, 6 December, is the municipal day of Oneşti.