Ernest Masoin (23 July 1844, Virton – 21 April 1915, Ixelles) was a Belgian physician and physiologist.
He then furthered his education in Paris, Bonn and Heidelberg, returning to Louvain in 1868 as successor to Louis-Antoine Van Biervliet (1802–1868) as chair of physiology, a position he would hold without interruption up until 1914.
During this time period, he was also a doctor at the Frères Alexiens asylum (from 1891), and in 1896, in addition to physiology, he began teaching classes in psychiatry at the university.
In 1903 he became part of the international commission to make presentations for the Nobel Prize in Medicine.
In 1915, the main avenue in front of the Hôpital Brugmann in the municipality of Jette was named in his honour.