Fellow actresses Caterina Murino, Eva Mendes, and Naomi Watts also attended Dolce and Gabbana's show.
Stefano Gabbana said of Scarlett, his latest muse: "She is beautiful."
Of the new collection, he added: "We felt the necessity to dream, to go beyond. Just like a woman in crisis, we put on more make-up."
The stars also turned out for the Extreme Beauty In Vogue exhibition in the Italian city.
The show consists of a series of images from the past 80 years of American Vogue by the greatest photographers of the 20th and 21st centuries.