is a Roman Catholic Diocese located in the municipality of Ipil in the Ecclesiastical province of Zamboanga in the Philippines. It is an ecclesiastical territory in the province of Zamboanga Sibugay. It occupies an area of 4,850 square kilometers extending from the boundary of Zamboanga del Norte on the north to Olutanga Island on the south, from the town of Tungawan on the west to the town Margosatubig on the east boundaries set by Pope John Paul II himself when he decreed the separation of this ecclesiastical territory from the Archdiocese of Zamboanga on December 24, 1979.