Ali Botush (Bulgarian: Али ботуш), also spelled Alibotoush, is a nature reserve in the small mountain range of Slavyanka, located on the border between Bulgaria and Greece. The reserve occupies the northern section of the mountain which lies within the territory of Bulgaria and takes its name from the old name of Slavyanka. It is situated in the municipalities of Sandanski and Hadzhidimovo, Blagoevgrad Province. It was declared in 1951 to protect the largest forests of the endemic Bosnian pine (Pinus heldreichii) in the Balkan Peninsula. Its territory was further expanded several times and spans an area of 1638 ha or 16,38 km2. It was declared a UNESCO Biosphere Reserve in 1977.