Mahakam Ulu Regency (Indonesian pronunciation: [maˈhakam ˈulu], lit. 'Upper Mahakam') is a regency (kabupaten) in the province of East Kalimantan, Indonesia. As the name implies, it comprises the upper valley of the Mahakam River. It covers an area of 18,427.81 km. The regency was established on 14 December 2012, formed from the former northern districts of West Kutai Regency. The districts now forming the regency held a combined population of 24,994 at the 2010 Census; the population for the new regency at the 2020 Census was 32,513; the official estimate as at mid 2023 was 38,498. The administrative capital is at Ujoh Bilang, which had 3,527 inhabitants as at mid 2022.

It is the only regency in East Kalimantan to share an international land border with the Malaysian state of Sarawak. Mahakam Ulu is also notorious for being geographically isolated from the rest of East Kalimantan. As a result, the public services and transportation access are still minimal.

The regency is divided into five districts (kecamatan), tabulated below with their areas and their populations at the 2010 Census and 2020 Census, together with the official estimates as at mid 2023. Notable settlements include the twin villages of Tiong Ohang and Tiong Bu'u in Long Apari District. The table also includes the locations of the district administrative centres, the number of administrative villages (all classed as kampung or desa) in each district, and its post code.

Kode Wilayah	Name of District (kecamatan)	Area in km	Pop'n Census 2010	Pop'n Census 2020	Pop'n Estimate mid 2023	Admin centre	No. of villages	Post code
64.11.03	Laham	2,903.97	2,275	2,749	3,125	Laham	5	75779
64.11.02	Long Hubung	1,457.66	6,405	8,604	9,085	Long Hubung	11	75770
64.11.01	Long Bagun	4,554.57	7,886	14,462	16,289	Ujoh Bilang	11	75767
64.11.05	Long Pahangai	5,057.40	4,326	4,978	5,353	Long Pahangai	13	75768
64.11.04	Long Apari	4,454.22	4,102	4,217	4,646	Long Ohang	10	75769
	Totals	18,427.81	24,994	35,010	38,498	Ujoh Bilang	50