"The name of this distinguished statesman is rightly considered the symbol of an era in modern world history," Putin said in a telegram to Cuban President Raul Castro cited by the Kremlin, AFP reported.
"Fidel Castro was a sincere and reliable friend of Russia."
The Cuban revolutionary leader, who built a communist state on the doorstep of the United States and for five decades defied US efforts to topple him, died on Friday.
Castro, in poor health since an intestinal ailment nearly killed him in 2006.