Beating 22 other films to the prize, the stomach-turning movie is the final instalment of Sokurov's cinematic series of four films on the nature of power, following his acclaimed portraits of Adolf Hitler, Vladimir Lenin and Emperor Hirohito.
Sokurov is the second Russian director ever to win the Golden Lion, after it was awarded to Andrei Zviaguintsev for "The Return" in 2003.
"There are films which make you dream, which make you cry, laugh and think, and there are films which change your life forever. This is one of those films," said jury head Darren Aronofsky, saying the decision had been unanimous.
The Silver Lion director award went to China's Cai Shangjun for his revenge tale 'People Mountain People Sea', in which a man ceaselessly hunts down his brother's killer.
The film was censured in China for revealing the appalling conditions in a Chinese mine.
Best actor was awarded to German-born Irishman Michael Fassbender,who plays an emotionally dysfunctional executive addicted to sex in Steve McQueen's powerful 'Shame'.
Best actress went to Deanie Yip for her portrayal of an elderly maid in a moving tale of the trials of growing old gracefully, 'A Simple Life'.
But the hotly-tipped favourites, including Roman Polanski's grotesque comedy of manners 'Carnage' and George Clooney's political thriller 'The Ides of March', went home empty handed, as did Tomas Alfredson's much praised 'Tinker, Taylor, Soldier, Spy'.
Twenty-three films competed in all in the Mostra, which saw a host of stars arrive by speed boat for the red carpet in the lagoon city, from Madonna to Gwyneth Paltrow, Kate Winslet, Jude Law and 'The Godfather' star Al Pacino.