Rein Aun (October 5, 1940 – March 11, 1995) was an Estonian athlete who represented the USSR. He competed in the decathlon, winning a silver medal in the 1964 Summer Olympics in Tokyo. He was 1.90 m (6 feet 3 inches) tall and weighed 86 kg (190 lbs). His trainer was Vladimir Zulin.
At the Tokyo Olympics, he earned a silver medal with 7,842 points, coming in second place between Willi Holdorf, who received the gold medal, and Hans-Joachim Walde, who received the bronze, both from the United Team of Germany.
His record of 7,898 points came on August 18, 1968, in Leninakan, Soviet Union (currently Gyumri, Armenia): 10.5 s - 7.07 m - 14.98 m - 1.83 m - 49.4 s - 15.2 s - 47.52 m - 4.30 m - 68.40 m - 4:38.6 min.