The Vilyuy (Russian: Вилю́й, Yakut: Бүлүү, Bülüü) is a river in Russia, the longest tributary of the Lena. About 2,650 kilometres long, it flows mostly within the Sakha Republic. Its basin covers about 454,000 square kilometres.
The main tributaries of the Vilyuy are the Ulakhan-Vava, Chirkuo, Chona, Chybyda, Ulakhan-Botuobuya, Ochchuguy-Botuobuya, Tangnary, Kempendyay, Tonguo and Bappagay on the right; and the Sen, Lakharchana, Akhtaranda, Ygyatta, Markha, Tyukyan, Kosmos and Tyung on the left.
