After the Kingdom of Romania entered World War I on the side of the Allies in August 1916, Macici fought in the Romanian Campaign. He commanded a machine-gun company from the 41st Infantry Regiment in the battles at Merișor and the Vulcan Pass. For these actions he was awarded in April 1917 the Order of Michael the Brave, 3rd class, and promoted to the rank of major. Later that year, at the Battle of Mărășești, he lost his right eye.