The 16th Century painting by Leonardo da Vinci is one of the world's most famous and valuable artworks, and is exhibited at the Louvre in Paris.
Footage shows two women crossing a security boundary to get closer to the painting, with both throwing soup towards the Leonardo da Vinci artwork.
Both are wearing a shirt with Riposte Alimentaire written on the front, referring to a climate activist group. A glass window protects the Mona Lisa, so the soup would not have damaged the painting itself.
Museum staff then rushed to the painting with black screens in a bid to block the public's view and asked visitors to evacuate the room immediately.
Riposte Alimentaire claims two people - aged 24 and 63 - involved with their "new campaign" were behind the incident to "demand the establishment of sustainable food social security".