Yulen (Bulgarian: Юлен) is a nature reserve in Pirin National Park, located in the homonymous mountain range in south-western Bulgaria.

[1] The flora consists of over 700 species of vascular plants; of them 44 are included in the Red Book of Bulgaria.

[1] Some of the important species are globeflower (Trollius europaeus), narcissus anemone (Anemone narcissiflora), Aquilegia aurea, lake quillwort (Isoetes lacustris) – the only place where this plant is found in Bulgaria,[3] Rhynchocorys elephas, curly sedge (Carex rupestris), etc.

[1] The most typical mammals in Yulen are brown bear, gray wolf and chamois.

Birds are of species conservation importance and include spotted nutcracker, jack snipe, western capercaillie, rock partridge, horned lark, golden eagle, northern goshawk, etc.