In 1800, Loison was posted to the Army of the Reserve to command a 5,300-man division and crossed the Great St Bernard Pass with Napoleon. He was wounded leading a failed assault on Fort Bard on 25 May 1800. Quickly recovering, he led his division in Guillaume Philibert Duhesme's corps in driving back Josef Philipp Vukassovich's command. He missed the Battle of Marengo because his men were busy capturing Milan and Cremona, while pursuing the Austrians eastward.