Sergey Viktorovich Diomidov (Russian: Сергей Викторович Диомидов; 9 July 1943 – 10 March 2024) was a Soviet gymnast who competed in the 1964 Summer Olympics and in the 1968 Summer Olympics.

He won team silver medals at both Games and a bronze on the vault in 1968.

[3] Between 1961 and 1967, Diomidov trained at the Army Forces Club in Tashkent, Uzbekistan.

In 1968, he moved to Moscow where he was coached by Konstantin Karakashyants at the CSKA club.

[6] Apart from his Olympic team medals, he was part of two silver medal teams at world championships, in 1966 and 1970; at the 1966 championships, he also won the gold on parallel bars.