The couple - who married in France last month - have been practising a form of Israeli self defence called Krav Maga to help them prepare for their upcoming movie By The Sea.
Brad, 50 - who has six children, Maddox, 13, Pax, 11, nine-year-old Zahara, eight-year-old Shiloh, and six-year-old twins Knox and Vivienne with his Maleficent star wife - is believed to have lost more than 10 pounds after participating in the intense military-style exercise classes for just three weeks and is even letting his kids join in the fun.
A source told the Daily Mirror newspaper: "The whole family are learning the moves, even the little ones are doing modified kids' moves but Brad has been doing it for 45 minutes a day and has dramatically lost weight and beefed up his muscles for the film."
Angelina Jolie and Brad Pitt in a scene from the film Mr & Mrs Smith.