A fire broke out at Maghaberry in the early hours of Tuesday morning.
A 29-year-old man was treated by a prison nurse for smoke inhalation after a fire occurred in a cell just after midnight in the prison.
Firefighters wearing breathing apparatus used a hosereel jet to deal with the small fire.
Fire fighters arrived at the scene around 12.08am.
Maghaberry Prison is a high security prison housing adult male long term sentenced and remand prisoners.