Nova Iguaçu (Portuguese pronunciation: [ˈnɔvɐ iɡwɐˈsu], locally: [ˈnɔv iɣwəˈsu] or [ˈnɔvə jɣwəˈsu], New Iguaçu) is a municipality in Rio de Janeiro state in Brazil.

The city is named after the Iguaçu River that runs through it and empties into Guanabara Bay (not to be confused with the Iguaçu River in Paraná state, which forms the Iguaçu Falls). It is part of the Greater Rio de Janeiro metropolitan area. It was the state's second largest city in population until Mesquita was split off, and now it is the fourth largest behind São Gonçalo, Duque de Caxias and the state capital, Rio de Janeiro. It lies northwest of Rio de Janeiro, in the centre of the northern part of its metropolitan area, Baixada Fluminense. The current mayor is Nelson Bornier (PMDB). The city is the seat of the Roman Catholic Diocese of Nova Iguaçu.