State television showed images of the former Cuban leader at a meeting with cheese experts near the capital, Havana.
Fidel Castro, 88, handed power to his younger brother Raul in 2006 after struggling to recover from illness.
His appearance comes days after Cuba and the US announced they were reopening embassies in each other’s capitals on July 20.
Fidel Castro is rarely seen in public, and secrecy about his health means his public appearances are scrutinized by the media.
The historic thaw between Cuba and the US was announced on December 17, in joint media conferences by Presidents Barack Obama and Raul Castro.
There was no immediate comment from Fidel Castro, and analysts said the rapprochement would not have happened if he was still in power.
Just over a month later, Fidel Castro broke his silence in a letter published on the Cuban Communist Party newspaper, Granma.
“I don’t trust the policy of the United States… but this does not mean I reject a pacific solution to the conflicts,” the Cuban leader wrote.
Relations had been frozen since the early 1960s when the US broke links and imposed a trade embargo on Cuba.
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