Nicaise de Keyser (26 August 1813 Zandvliet - 17 July 1887 Antwerp), was a Belgian painter of portraits and historical paintings.

He received his painting instruction at the Antwerp Academy of Fine Arts under Joseph Jacobs and Bree, before leaving for Italy in 1839. He married the genre painter Isabella Telghuys on 6 October 1840.

His painting of the Battle of the Golden Spurs, which was exhibited at the Brussels Salon in 1836, shows the French commander, Robert II of Artois, surrendering his sword shortly before being slaughtered by the Flemish infantry. Seeing the painting is said to have inspired Hendrik Conscience to write his book "De Leeuw van Vlaanderen" (The Lion of Flanders) and give the starring role to Robert III of Flanders, who had been nowhere near the battle. The success of de Keyser's work led shortly after to his less impressive work, the Battle of Worringen of 1288.

In 1855 de Keyser succeeded Gustave Wappers on his dismissal as director of the Antwerp Academy. Starting in 1862 de Keyser depicted the Flemish School in a series of decorative paintings, destined for the Antwerpse Museum and Academy. These works were moved at the end of the nineteenth century, to the new Royal Academy of Fine Arts in Antwerp. In 1873 de Keyser was awarded the Prussian "Pour le Mérite".