Thomassin may refer to:
People Surnames Claude Thomassin, French bow maker, or Archetier Florence Thomassin, French actress and sculptor Laurie Thomassin, French retired breaststroke swimmer Louis Thomassin, French theologian and Oratorian Antoine de Thomassin de Peynier (1731–1809), officer of the French Royal Navy
Places Thomassin, a neighborhood of Pétion-Ville, Haiti