 The State of Vietnam referendum of 1955 determined the future form of government of the State of Vietnam , the nation that was to become the Republic of Vietnam ( widely known as South Vietnam ) . It was contested by Prime Minister Ngô Đình Diệm , who proposed a republic , and former emperor Bảo Đại . Bảo Đại had abdicated as emperor in 1945 and at the time of the referendum held the title of head of state . Though published counts showed Diệm winning the election with 98 @.@ 2 % of the vote , the referendum was widely marred by electoral fraud . In the capital , Saigon , Diệm was credited with more than 600 @,@ 000 votes , although only 450 @,@ 000 people were on the electoral roll . He accumulated tallies in excess of 90 % of the registered voters , even in rural regions where opposition groups prevented voting . 
