The small painting, entitled “The Arabs of Oran”, measuring 19 centimetres wide and 15 centimetres high, was reportedly lifted from a wall on Friday and taken out by someone on foot.
The artwork, dating from 1833, was displayed at a gallery in the Rue Saint-Honoré across the road from the Louvre Museum in the centre of Paris.
A gallery worker discovered the theft on Friday afternoon.
Delacroix, who lived from 1798 to 1863, was the most important member of the French Romantic movement.
The anti-crime squad of the Paris judicial police is looking into the theft.