The territory was formerly part of the Apostolic Vicariate of Napo (q.v.), which bordered Colombia. In 1916 the governments of Ecuador and Colombia fixed the boundaries between the two countries. It therefore became necessary to align civil and ecclesiastical boundaries. On 16 April 1924 the Sacred Congregation for the Propagation of the Faith ceded to the Apostolic Vicariate of Napo the area of the Apostolic Prefecture of Caquetá that had passed to Ecuador and erected into the Apostolic Prefecture of San Michele de Sucumbios the northern part of Napo lying between the Río Sucumbios and the political boundary with Colombia to the northeast, and the Río Aguarico and Río Napo to the southwest.
It has an area of 67,120 sq km, with a population of 13,200 Catholics and 2,500 pagans. There are 4 missionaries and 4 sisters. Elementary schools: 2.