The men's 66 kg competition in judo at the 2016 Summer Olympics in Rio de Janeiro was held on 7 August at the Carioca Arena 2.

The gold and silver medals were determined by a single-elimination tournament, with the winner of the final taking gold and the loser receiving silver.

Judo events awarded two bronze medals.

Quarterfinal losers competed in a repechage match for the right to face a semifinal loser for a bronze medal (that is, the judokas defeated in quarterfinals A and B competed against each other, with the winner of that match facing the semifinal loser from the other half of the bracket).

[1] The medals for the competition were presented by Beatrice Allen, a Gambian member of the International Olympic Committee, and the gifts were presented by Yasuhiro Yamashita, International Judo Federation executive committee member.