The ailing 82-year-old former leader met Wednesday with Argentine President Cristina Fernandez.
Castro wrote in a statement posted on a government Web site hours later that he "did not have the slightest doubt of the honesty of Obama ... when he expresses his ideas."
The meeting and essay dispelled rumors that Castro's health had taken a turn for the worse.
He normally published his ruminations a few times a week but had not released an essay since Dec. 15, fueling speculation he could have lapsed into a coma.
THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.
HAVANA (AP) — Fidel Castro watched the U.S. inauguration on television and said Wednesday that Barack Obama seems "like a man who is absolutely sincere," Argentina's president said after meeting with the ailing Cuban icon.
"Fidel believes in Obama," Cristina Fernandez said.
The meeting with Fernandez, just before she ended a four-day visit to Cuba, dispelled persistent rumors that the 82-year-old Castro had suffered a stroke or lapsed into a coma in recent days.
"I was with Fidel about an hour or more," she told reporters at the airport as she left. "We were chatting, conversing. He looked good."
Fernandez said Castro wore the track suit that has become his trademark since he fell ill in July 2006 and vanished from public view. A spokesman said the two met alone.
"He told me he had followed the inauguration of Barack Obama very closely, that he had watched the inauguration on television all day," Fernandez said. "He had a very good perception of President Obama."
Fernandez said Castro called Obama "a man who seems absolutely sincere," who believes strongly in his ideas "and who hopefully can carry them out."
Raul Castro, who took over the presidency from his brother, appeared with Fernandez, scoffing at the rumors about his brother's health.
"Do you think if he were really gravely ill that I'd be smiling here?" Raul Castro said. "Soon I'm going to take a trip to Europe. You guys think I could leave here if Fidel were really in grave condition?"
Castro, 77, said his older brother spends his days "thinking a lot, reading a lot, advising me, helping me."
The rumors about Castro's health were fanned by the fact that he hasn't written a newspaper column in more than a month and hadn't held a confirmed meeting with a foreign leader since Nov. 28. The presidents of Panama and Ecuador visited this month but left without saying they had seen the elder Castro.
"Now you know that Fidel is fine, and not like the rumors around here," Raul Castro said.
Earlier Wednesday, Raul Castro said Obama "seemed like a good man" and wished him luck.
Obama has pledged to ease limits on Cuban-Americans' visits to the island and on how much money they can send home to relatives. He has also offered to negotiate personally with Raul Castro, though he has said he won't push Congress to lift the U.S. trade embargo, at least not right away.
Cubans see those as important steps in improving U.S.-Cuba relations. Obama's predecessor, George W. Bush, tightened sanctions on the communist-governed country.
The comments by the Castro brothers contrast with those of their ally, Venezuelan President Hugo Chavez, whose government took exception to Obama's characterization of Chavez as "a destructive force in the region." Obama made the comments in an interview with the Univision television network.
"President Chavez has won 12 of the 14 elections in the past 10 years," the state-run Bolivarian News Agency quoted Maduro as saying. "He is the legitimate president."