Ambrose Joseph Small (February 11, 1866 – disappeared December 2, 1919) was a Canadian theatre magnate who owned several Ontario-based theatres including the Grand Opera House in Toronto, the Grand Opera House in Kingston, the Grand Theatre in London, and the Grand Theatre in Sudbury. The last known sighting of Small occurred the evening of 2 December 1919. He had been known to travel without notice, so his disappearance was not reported until early 1920. His body was never recovered.