The Roman Catholic Diocese of Nicolet (Latin: Dioecesis Nicoletana) (erected 10 July 1885) is a suffragan of the Archdiocese of Sherbrooke, Quebec, Canada.

The seat of the bishop (or "ordinary") is the Cathedral of St. Jean-Baptiste, a spectacular building opened in 1963, which seats 1,200 worshippers and features extensive stained glass as well as other artwork by a number of local artists.

The present building is the fifth cathedral, successor to four previous buildings that fell victim to various physical disasters: two collapses, a fire, and damage from the Nicolet landslide of 1955.

A frieze of stained glass in the apse shows characters from the Bible and from the history of the Christian church, including a portrait of Bishop Martin, who was responsible for construction of the new building.

This article about a Roman Catholic diocese in Canada is a stub.