"The Vietnamese people have closely followed the recent progress of the president's health and are happy to hear that he has recovered after the surgery," said Pham The Duyet, president of the communist nation's Fatherland Front.
"I would like to send President Fidel Castro the friendliest sentiments from the Vietnamese people. Wishing you a recovery soon to continue leading Cuba's revolution to new victories," said the front, the largest mass organisation in Vietnam.
In another message, the Vietnam Union of Friendship Organisations also paid tribute to Castro.
"President Fidel Castro is not only a prominent leader of the Cuban people but also a symbol of strong-hearted revolutionary will and lofty international unity and a great and faithful friend of the Vietnamese people," it said.
Vietnam and Cuba, two of the world's last communist regimes, maintain close political and economic links dating back to the Vietnam War era when Havana was a staunch ally of Hanoi.
Castro's last visit to Vietnam was in February 2003.
Cuba marked Fidel Castro's 80th birthday Sunday by releasing photos of the communist leader which erased any doubt that he made it through major surgery.