The Aldan (Sakha and Russian: Алдан) is the second-longest right tributary of the Lena in the Sakha Republic in eastern Siberia. The river is 2,273 kilometres long, of which around 1,600 kilometres is navigable. It has a drainage basin of 729,000 square kilometres.
The river was part of the River Route to Okhotsk. In 1639 Ivan Moskvitin ascended the rivers Aldan and Maya and crossed to the Ulya to reach the Sea of Okhotsk.
Its basin is known for gold and for Cambrian fossils.
