Southwest Sumba Regency () is a regency on Sumba Island in East Nusa Tenggara province of Indonesia. Established on 2 January 2007 out of parts of West Sumba Regency, the regency has its seat (capital) in Tambolaka (part of the town of Waitabula in the north), while Bondokodi in the largest village in the west. Its population was 283,818 in the 2010 decennial census and had risen to 303,650 at the 2020 census; the official estimate as at mid 2024 was 335,500 (comprising 171,513 males and 163,987 females.
The Southwest Sumba Regency when created was composed of eight districts (kecamatan), but since 2010, three additional districts have been created within the Regency, by the splitting of existing districts. The areas (in km<sup>2</sup>) and the populations of the districts at the 2010 census and the 2020 census are listed below, together with the official estimates as at mid 2025. The table also includes the locations of the district administrative centres, and the number of administrative villages in each district (totaling 173 rural desa and 2 urban kelurahan - the latter both in Kota Tambolaka District).
Notes: (a) The 2010 census populations of Kodi Balaghar is included with the figures for Kodi Bangedo, from which it was split.<br />(b) including the desa of Wee Wella, which is an exclave separated from the rest of the district by a detached part of Kota Tambolaka District. <br />(c) The 2010 census populations of Kota Tambolaka and Wewewa Tengah Districts are included with the figures for the districts from which they were split. <br />(d) including the desa of Wee Kambala, which is an exclave separated from the rest of the district by Kota Tambolaka District. <br />(e) including the two kelurahan of Waitabula (which includes the regency capital of Tambolaka, the former community of Radamata and the main airport) and Langga Lero (adjoining Waitabula to the south); the district also includes the desa of Kalembu Kaha, which is an exclave separated from the rest of the district by Wewewa Barat and Kodi Utara Districts.
The Kalaki Kambe desa (of Wewewa Barat District) forms a salient from the rest of that district towards the north coast of Sumba island, reaching the coast between the desa of Wee Wella (an exclave of Kodi Utara District) and Kalembu Kaha (an exclave of Kota Tambolaka District) to the west and the desa of Wee Kambala (an exclave of Loura District) to the east. The populations in 2023 of these detached desa (which together form a non-administrative grouping along the northcoast of the regency) were as follows:
Several tourist attractions in this district have been widely explored and visited by a variety of local and foreign tourists, but there are only a few who have access to roads and adequate facilities and infrastructure available, namely Mananga Aba Beach, Mbawana beach, Oro Beach, Kawona Beach, Newa Beach, Pantai Waikelo, Sumba Cultural Home, Lake Saltwater Weekuri, and Pabeti Waterfall.
This district includes several traditional villages such as Wainyapu and on the south-west coast, and others inland. Wainyapu is particularly rich in dolmens, which - as of 2021 - are still built for collective graves.