On April 12, 1961, Gagarin became the first human to travel into space and orbit the Earth. His historic flight aboard the Vosktok-one capsule lasted 108 minutes.
Tuesday's commemoration comes three days before the scheduled launch of a Russian rocket carrying the next two-man crew to take over duties aboard the International Space Station.
Russian cosmonaut Sergei Krikalev and American astronaut John Phillips are due to blast off from Kazakhstan's Baikonur cosmodrome on Friday.
Meanwhile, a recent poll by the National Public Opinion Study Center indicates that two out of three Russians think the country should do everything possible to remain a leading space power.