The 35-year-old model-actor has been dating his former 'That '70s' show co-star Kunis since 2012, reported People magazine.
The couple were spotted exploring the city in a horse-drawn carriage.
"They seemed very much in love. They were holding hands, they were giving kisses to each other," a source said.
The duo visited the local markets and famous chocolate shops before enjoying a meal at Carmelite restaurant.
"Mila ate a local dish called Hoppescheuten, which she had never heard of but wanted to try. She just thought 'why not?' and thought it was wonderful.
Prior to their weekend in Bruges, Kutcher and Kunis joined Channing Tatum and his pregnant wife, Jenna Dewan-Tatum for a Opera show on Friday.
