The 38-year-old, who has won stages in the Giro d'Italia and Tour de France during his career, will continue his career with Bjarne Riis' squad.
"I'm very happy that I'm going to ride another year with this team, because it simply feels great to be here. I like the atmosphere and the way we approach the races," Tosatto, who finished seventh in this year's Paris-Roubaix, said.
"Next year we will have an even stronger team, and this just motivates me more to compete in the biggest races. My main objectives will be pretty much the same as in the last two seasons, to do well in the cobbled classics and help Alberto (Contador) to win in the Grand Tours."
Portuguese climber Bruno Pires, who rode in support of Alberto Contador at the Vuelta a Espana, has also penned a new one-year contract.