Men's 81 kg competition in judo at the 2012 Summer Olympics in London, United Kingdom, took place at ExCeL London.

[1] 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).

[2] All times are British Summer Time (UTC+1)