Members of the Black Caucus described Castro as healthy and energetic. Castro's wife was also at the meeting which took place at Castro's home, which was described by congressman rush, as very modest.
Coming after lawmakers met with his brother Raul, the current president, the session appeared to underscore the Cuban government's desire for improved relations with the United States under new President Barack Obama.
Greg Adams, a spokesman at the U.S. Interests Section in Havana, said Rep. Barbara Lee, a California Democrat, and two other lawmakers met with the 82-year-old Castro.
Lee led a delegation of six Democratic representatives who left Havana after a five-day visit designed to encourage dialogue between the U.S. and Cuba.
Adams said he expected the Cuban government to release more information about the meeting in state television's nightly newscast.
Castro, who clashed with every U.S. president since Dwight D. Eisenhower, has not been seen in public since undergoing emergency intestinal surgery in July 2006. He turned over his duties to his brother, five years his junior, then formally ceded power in February.
Raul Castro met with the six American legislators for more than four hours Monday night, his first face-to-face discussions with U.S. leaders since he became Cuba's president -- a sign that both countries may be serious about improving nearly 50 years of frigid relations.
The visit to Cuba came as the Obama administration conducts a broad review of its policy toward the communist nation -- and as some U.S. lawmakers press for an end to the travel bans that have prevented Americans from visiting the island.
After the delegation's talks with Raul Castro, Lee said the meeting was constructive and the lawmakers would prepare a detailed look at everyday life in Cuba for the White House.
"We talked about all the issues necessary to normalize relations between our two countries," she said.
The 77-year-old Raul Castro, who holds the rank of four-star army general, wore a business suit instead of his trademark olive-green fatigues for the closed-door meeting that ended around midnight.
"I'm convinced Raul Castro wants a normal relationship with the United States," Lee told The Associated Press. "He's serious."
Delegation members said they discussed topics such as increased U.S.-Cuba trade and better cooperation in combating drug and human trafficking. But "we did not talk about specifics," Lee said at a news conference.
She did not answer questions about why the delegation failed to meet with any Cuban dissidents. Some past congressional trips to Cuba, though not all, have included meetings with opposition figures.
The Cuban government issued a statement calling the encounter "a broad exchange of ideas on many topics, with emphasis on the future evolution of bilateral relations and economic ties after the arrival of a new U.S. administration."
The meeting came the same day that Jeffrey Davidow, the White House adviser for the upcoming Summit of the Americas, said Obama will soon move to ease travel and financial restrictions on Cuba.
A commentary by Fidel Castro in state newspapers Monday said that Cuba is not afraid to talk directly to the United States and that the communist government does not thrive on confrontation as its detractors have long claimed.
Both Castro brothers have said for decades that they would be willing to talk personally with U.S. leaders. Currently, the countries do not have formal diplomatic relations.
In a second column posted late Monday night on a government Web site, the ex-president saluted the American legislators for traveling to the island, saying he "values the gesture of the legislative group."
"They are witnesses to the respect with which Americans who visit our homeland are always received," Fidel Castro wrote.
Lawmakers in both houses of Congress have proposed to largely eliminate bans on travel to Cuba, effectively lifting a key component of the embargo. The visiting representatives said they would support those efforts.
The Associated Press contributed to this report.