The Roman Catholic Diocese of Campo Maior (Latin: Dioecesis Campi Maioris) is a Latin suffragan diocese in the ecclesiastical province of Teresina, in northeastern Brazil's Piauí state.

Its cathedral episcopal see is Catedral Santo Antônio, dedicated to Saint Anthony, in the city of Campo Maior, Piauí.

• Established 12 June 1975 as Diocese of Campo Maior on territories split off from the Diocese of Parnaíba and its Metropolitan Archdiocese of Teresina

As per 2014, it pastorally served 354,000 Catholics (94.9% of 373,000 total) on 27,943 km in 31 parishes and 419 missions with 35 priests (34 diocesan, 1 religious), 1 deacon, 23 lay religious (1 brother, 22 sisters) and 10 seminarians.

(all Roman rite)

Suffragan Bishops of Campo Maior

• Abel Alonso Núñez, Mercederians (O. de M.) (1976.03.24 – retired 2000.02.02), previously Auxiliary Bishop of the then Territorial Prelature of Bom Jesus do Piauí (Brazil) (1971.07.14 – 1976.03.24) & Titular Bishop of Nicives (1971.07.14 – 1976.03.24)
• Eduardo Zielski (2000.02.02 – 2016.03.02), next Bishop of São Raimundo Nonato, Piaui (2016.03.02 - present)
• Francisco de Assis Gabriel dos Santos, Redemptorists (C.SS.R.) (2017.06.21 – ...), no previous prelature.

So far, the diocese has had no auxiliary bishop.

• Juarez Sousa Da Silva, appointed Bishop of Oeiras, Piaui in 2008

• List of Catholic dioceses in Brazil

• GCatholic.org, with Google map - data for all sections
• Catholic Hierarchy

4°49′26″S 42°10′06″W / 4.8238°S 42.1684°W / -4.8238; -42.1684