The Roman Catholic Diocese of Rancagua (in Latin: Dioecesis Rancaguensis) is a suffragandiocese of the Archdiocese of Santiago de Chile. The diocese was established on 18 October 1925 as Diócesis de Santa Cruz de Rancagua, by Pope Pius XII by means of the papal bullApostolici muneris ratio.
The diocese comprises the three provinces of the O'Higgins Region of Chile: Cachapoal, Colchagua and Cardenal Caro, with the exception of the comuna of Navidad, of the latter province, which belongs to the diocese of Melipilla. It covers a territory of 16,042 km2 (6,194 sq mi) and has 63 parishes. It is estimated that 80 percent of the population of the diocese is Catholic. This figure represents about 625,000 Catholics out of a total population of 781,000 persons.