Eugène Michel Antoniadi (Greek: Ευγένιος Αντωνιάδης; 1 March 1870 – 10 February 1944) was a Greek-French astronomer. He is known for creating the Antoniadi scale as well as for his observations of the planets, and was a major opponent of the notion of Martian canals. He created some of the most detailed maps of Mars at the time, and many features on the planet are still known by the names he suggested. He also created the first map of Mercury, though it turned out to be incorrect.

Antoniadi was born in Istanbul (Constantinople) but spent most of his adult life in France after being invited there by Camille Flammarion.

He became a Fellow of the Royal Astronomical Society on 10 February 1899, and in 1890 he became one of the founding members of the British Astronomical Association (BAA). In 1892, he joined the BAA's Mars Section and became that section's Director in 1896.

He became a member of the Société astronomique de France (SAF) in 1891.

Flammarion hired Antoniadi to work as an assistant astronomer in his private observatory in Juvisy-sur-Orge in 1893. Antoniadi worked there for nine years. In 1902, he resigned from both the Juvisy observatory and from SAF.

Antoniadi rejoined SAF in 1909. That same year, Henri Deslandres, Director of the Meudon Observeratory, provided him with access to the Grande Lunette (83-cm Great Refractor)

He became a highly reputed observer of Mars, and at first supported the notion of Martian canals, but after using the 83 centimeter telescope at Meudon Observatory during the 1909 opposition of Mars, he came to the conclusion that canals were an optical illusion. He also observed Venus and Mercury.

He made the first map of Mercury, but his maps were flawed by his incorrect assumption that Mercury had synchronous rotation with the Sun. The first standard nomenclature for Martian albedo features was introduced by the International Astronomical Union (IAU) when they adopted 128 names from the 1929 map of Antoniadi named La Planète Mars.