Alexis de Castillon (born Marie-Alexis de Castillon de Saint-Victor) (13 December 1838, in Chartres – 5 March 1873, in Paris) was a French composer of classical music.
Son of an old family of the Languedoc nobility, and initially intended by his parents for a military career, Castillon gave up plans for professional soldiering in favor of music, which he learned first in his birthplace and then in Paris, studying piano and composition. In this second capacity he went to the Paris Conservatoire; there he attended the class of Victor Massé and later, from 1869, that of the more distinguished César Franck. It was under Franck's aegis that Castillon composed his Opus 1, a piano quintet (he disavowed earlier efforts, including a symphony in F major which he had written in 1865).

In fragile health at the best of times (volunteering during the War of 1870, he fell ill and was demobilized in 1871), he died of complications from fever in 1873, before even reaching the age of 35. He nevertheless had time to compose several impressively Romantic works (bearing above all the influence of Robert Schumann). These works included pieces for piano, chamber music, mélodies, a piano concerto, and Symphonic Sketches. As well as writing music, he took part in Parisian musical life, in particular helping to create, in 1871, the Société Nationale de Musique of which he was the first secretary.