Aksu-Jabagly Nature Reserve (Kazakh: Ақсу-Жабағылы мемлекеттік табиғи қорығы) is the first and oldest nature reserve in Kazakhstan.

Located at the western end of the Talas Alatau mountain range in the Tulkubas, Tolebiy, and Baidibek districts of the Turkestan region, as well as in the Zhuldyz district of the Zhambyl region, the reserve covers a total area of 131,934 hectares.

The Aksu-Jabagly Reserve was established by decrees of the Kazakh SSR People's Commissars Council on July 14, 1926, and the RSFSR People's Commissars Council on May 27, 1927, on an area of 30,545 hectares. In 1929, the canyon of the Aksu River was added to the reserve. The reserve was created “with the aim of preserving intact the Aksu and Jabagli rivers and all their tree and shrub plantings, herbaceous cover, and the wildlife inhabiting this area — as a natural monument.” In 1935, the area was increased to 48,570 hectares by adding the valleys of the Bala-Baldybrek and Baldybrek rivers.

On November 17, 2005, the Government of the Republic of Kazakhstan issued a decree granting the land for permanent use to the state institution “Aksu-Jabagly Nature Reserve,” managed by the Forest and Hunting Committee of the Ministry of Agriculture of Kazakhstan. As a result, the reserve's area increased to 57,774 hectares. The reserve covers the majority of the northwestern end of the Talas Alatau and the adjacent section of the Ugam mountain range, extending into the southeastern part of the South Kazakhstan and Zhambyl regions. A branch of the reserve, the paleontological site Karabastau (126 hectares), is located 120 km northwest, in the Boroldai mountain range of the Syrdarya Karatau. A second paleontological site, Auliye, has an area of 100 hectares.

The flora of the Aksu-Jabagly Reserve includes 1,737 species, including 235 fungi, 64 lichens, 63 species of algae and mosses, and 1,309 higher plants from 481 genera and 91 families. The richest families by species composition include: Asteraceae (215 species from 74 genera), Leguminosae (128 species), Poaceae (116 species), Rosaceae (69 species), Umbelliferae (67 species), Lamiaceae (64 species), Caryophyllaceae (56 species), Cruciferae (53 species), Ranunculaceae (48 species), Scrophulariaceae (45 species), Boraginaceae (40 species), and Liliaceae (34 species).

The fauna of fish includes 7 species, the most typical being the ordinary marinka (Schizothorax intermedius) and the naked osman (Diptychus dybowskii).

There are 11 species of reptiles and 3 species of amphibians in the reserve, which make up more than 70% of the regional fauna of these groups, with 3 species listed in Kazakhstan’s Red Book. Of particular concern for conservation is the legless lizard, the yellow-bellied skink.

Among the vertebrate animals, birds are the most numerous, with 247 species. Of these, 130 species breed in the reserve, including 41 resident species. Additionally, 80 species are migratory (spring and autumn), 19 species are wintering, and 18 species are irregular visitors. Eleven species are listed in the Red Book of Kazakhstan, and two species are recognized by IUCN as globally threatened — the Corncrake (Crex crex) and the White-winged Woodpecker (Dendrocopos leucopterus).

The reserve is home to 52 species of mammals, which constitute 80% of the mammalian fauna of the Western Tien Shan. These include rodents (44%), carnivores (24%), bats (18%), ungulates (9%), hares, and insectivores (3% each). Ungulates in the reserve include the argali, mountain goat, roe deer, maral, and wild boar, while carnivores include the bear, badger, stone marten, weasel, and stoat. Rodents and lagomorphs include the long-tailed marmot, porcupine, Tolai hare, and muskrat.

Ten species of rare and endangered mammals are listed in the Red Book of Kazakhstan. Three mammal species are of particular conservation concern: the snow leopard, listed as a threatened species by IUCN, the endemic western Tien Shan species of marmot (Menzbier’s marmot), and the currently endangered subspecies of argali.

On June 12, 2015, the Aksu-Jabagly Reserve was included in the UNESCO World Heritage list.