Guillaume de Sax (1889–1945) was a Belgian actor.

De Sax was born Guillaume Henri Robert de Segur Lamoignon in Belgium and died in France. He was married to the actress Cécile Sorel.

Partial filmography

• Ernest the Rebel (1938)
• Three Waltzes (1938)
• I Was an Adventuress (1938)
• Coral Reefs (1939)
• Immediate Call (1939)
• Angelica (1939)
• Cristobal's Gold (1940)
• Sins of Youth (1941)
• Miss Bonaparte (1942)
• The Lover of Borneo (1942)
• No Love Allowed (1942)
• Twisted Mistress (1942)
• Strange Inheritance (1943)
• La Main du diable (1943)
• Picpus (1943)
• Vautrin (1943)
• Farandole (1945)
• The Eleventh Hour Guest (1945)