The 27-year-old starlet was dinning at Mexican restaurant Bodega Negra when she saw Danny Franzese, the actor who plays "Damian" in the 2004 film.
A source tells Us Weekly that the pair spotted each other across the restaurant and "chatted for a while before walking out together," the co-stars shared several hugs and were reportedly happy to pose for fan photos.
"Everyone was so excited to see Cady and Damian reunite again and pose for pictures," the source added.
The actress later posted a picture of the moment on her Instagram account.
Lohan and Franzese's reunion comes on the verge of the film's 10th anniversary -- Mean Girls was released on April 30, 2004. To commemorate the landmark, director Mark Waters shared 10 secrets about the film with Vulture.
Among them are the fact that Lohan and Rachel McAdams auditioned for each other's roles, but Waters ended up picking the Feaky Friday star for the lead because of her age.
"When Lindsay was acting with Rachel, she got very shy, because Rachel was older and a very accomplished actress," said Waters. "She'd come in the room and not talk to Lindsay -- she was very focused. Lindsay kind of got nervous around her, and I thought that, more than anything, was going to be the deciding factor, the fact that she affected Lindsay in that way."
Other shockers include that Amanda Seyfried also auditioned for the Regina George role; that the famous four-way phone sequence was shot at completely different times; and that Amy Poehler coached the actor who played Kevin Gnapoor on how to rap.