Henri Eugène Augustin Le Sidaner (7 August 1862 – July 1939) was an intimist painter.

Sidaner was born to a French family in Port Louis, Mauritius. In 1870 he and his family settled in Dunkirk. Le Sidaner received most of his tutelage from the École des Beaux-Arts under the instruction of Alexandre Cabanel but later broke away due to artistic differences.

Between 1885 and 1894 Le Sidaner lived the year round at the Etaples art colony and was joined there by his childhood friend Eugène Chigot (1860–1923), who shared his interest in atmospheric light. Later Le Sidaner traveled extensively throughout France. He also visited many cities around the globe, as well as villages throughout Europe. He exhibited at the Salon, the Galeries Georges Petit in Paris and the Goupil Gallery in London, and settled in Gerberoy.

Marcel Proust's mention of Le Sidaner's work in his novel In Search of Lost Time confirms its later reputation. In Sodom and Gomorrah, the narrator mentions that an eminent barrister from Paris had devoted his income to collecting the paintings of the "highly distinguished" but "not great" Le Sidaner.