These are the rosters of all participating teams at the men's water polo tournament at the 2020 Summer Olympics in Tokyo. The twelve national teams were required to submit squads of 12 players. Additionally, teams could name one alternate player. In the event that a player on the submitted squad list suffered an injury or illness, that player would be able to be replaced by the player in the alternate list. On 3 July 2021, the International Olympic Committee (IOC) confirmed that there was a change for the 2020 Summer Olympics, allowing all 13 water polo players named to be available on the roster, with 12 being named for each match. This change was implemented due to the challenges of the COVID-19 pandemic. As of 2 August 2021, all players competed in the men's tournament.