Lev Stepanovich Demin (Russian: Лев Степанович Дёмин; born January 11 1926 in Moscow, died December 18, 1998 in Zvyozdny Gorodok ) was a Soviet cosmonaut who flew on the Soyuz 15 mission.

Demin gained a doctoral degree in engineering from the Soviet Air Force Engineering Academy and the rank of Colonel in the Soviet Air Force.

He only made a single spaceflight before resigning from the space programme in 1982 and taking up deep-sea research.

He died of cancer in 1998.