The Archdiocese of Niteroi (Nictheroy) (Latin: Archidioecesis Nictheroyensis) is a Latin Church ecclesiastical territory or archdiocese of the Catholic Church in the city of Niterói in Rio de Janeiro state, southeast Brazil.

Its cathedral archiepiscopal see is Metropolitan Cathedral of St. John the Baptist, dedicated to John the Baptist, in Niterói.

The city also has a Minor basilica : Basílica Nossa Senhora Auxiliadora, dedicated to Our Lady of Perpetual Help, and builds a future Cathedral: Nova Catedral São João Batista Nova Catedral São João Batista.

As per 2014, it pastorally served 1,228,000 Catholics (53.8% of 2,283,000 total) on 4,728 km² in 77 parishes and 6 missions with 147 priests (105 diocesan, 42 religious), 75 deacons, 249 lay religious (50 brothers, 199 sisters) and 74 seminarians.

The suffragan sees in Niterói's ecclesiastical province are :