Mothiba, who scored on the opening day of the season, has put pen to paper on a five-year deal with Strasbourg.
"Work hard at training and always give my best. Life is beautiful, I am lucky to be a footballer so I have to enjoy every moment," Mothiba told the club's official website.
"I am very happy to sign at Racing. I will give everything to the club, work hard every day and try to score a lot of goals to make people happy!"