The Diocese of Mayagüez (Latin: Dioecesis Maiaguezensis) is a Latin Church ecclesiastical territory or diocese of the Catholic Church in the United States and consists of the western part of the island of Puerto Rico, an American commonwealth.

The diocese is led by a prelate bishop, who pastors the motherchurch in the City of Mayagüez, Catedral Nuestra Señora de la Candelaria in front of the Plaza Colón.

The See of Mayagüez was canonically erected on March 1, 1976, and is a suffragan diocese of the Metropolitan Province of San Juan de Puerto Rico.

Its jurisdiction includes the municipalities of Aguadilla, Rincón, Aguada, Moca, San Sebastián, Añasco, Mayagüez, Las Marías, Maricao, Hormigueros, Cabo Rojo, San Germán, and Sabana Grande.

On 7 September 2018, Judge Edward Godoy ruled that the bankruptcy filed by the Archdiocese of San Juan would also apply to every Catholic diocese in Puerto Rico, including Mayagüez, and that all would now have their assets protected under Chapter 11.