Mattis visited the US base to offer holiday greetings to American troops stationed there and did not tour the notorious US detention facility, the Associated Press reported on Thursday.
Donald Rumsfeld was the last US defense secretary to visit Guantanamo in January 2002, just weeks after the arrival of the first prisoners.
Inaugurated by former President George W. Bush, the US detention center in Cuba housed nearly 800 prisoners detained in the wake of September 11, 2001, terrorist attacks in the United States.
"Secretary Mattis is currently visiting with troops at Guantanamo Bay for the holidays to thank them for their service", Pentagon spox tells @CNN— AnneClaire Stapleton (@AnneClaireCNN) 21 декабря 2017 г.
Former President Barack Obama sought to close the prison, but 41 prisoners remained when Trump took office.
Trump has not yet released any new inmates, but nor has he added to their numbers, despite his campaign pledge to "restock" Guantanamo with new terrorists.
Attorney General Jeff Sessions, Deputy Attorney General Rod Rosenstein and Director of National Intelligence Dan Coats visited Guantanamo in July 2017.