Denis van Alsloot or Denijs van Alsloot was a Flemish landscape and genre painter, draughtsman and tapestry designer. He was employed as a court painter and worked for the local elite in Brussels. He is considered to be a member of the Sonian Forest school of landscape painters, which included landscape painters such as Jacques d'Arthois and Cornelis Huysmans. These painters working in Brussels had a preference for depicting scenes from the Sonian Forest near Brussels. Van Alsloot was also a specialist in depicting civil processions, local festivals and ceremonies.

Van Alsloot was born in Mechelen or possibly Brussels. His father was a tapestry worker. It is not known who was his teacher. He is first recorded in official records when he joined the Brussels Guild of St Luke in 1599 as a tapestry designer. He also took his first pupil in 1599. He trained a further three apprentices between 1599 and 1625. Van Alsloot was exclusively working on the design of tapestries until 1606, the year in which he signed his first painting.

Alsloot's career started to take off from the early 17th century after he was appointed court painter to Albert and Isabella, the governors of the Spanish Netherlands. He became a painter to the elite and served a clientele of princes, courtesans and influential state officials.

He was still alive in 1626 as is testified by a painting dated in that year. He must have died in or before 1628 as two works he had left as inheritance to a niece were bought in 1628 by the Archduchess Isabella.