The Roman Catholic Diocese of Tumaco (Latin: Tumacoënsis) is a suffragan Latin diocese in the ecclesiastical province of Popayán, in southwestern Colombia.

Its cathedral episcopal see is the Catedral San Andrés, dedicated to Saint Andrew, in the city of Tumaco, Nariño Department.

As per 2014, it pastorally served 249,520 Catholics (74.4% of 335,320 total) on 16,000 km2 in 17 parishes with 31 priests (19 diocesan, 12 religious), 9 deacons, 39 lay religious (26 brothers, 13 sisters) and 7 seminarians.

(all Roman rite)