Firefighters were called to the first-floor property in Portobello, Edinburgh, at around 5.20am yesterday.
A spokeswoman for Lothian and Borders Fire and Rescue said six firefighters wearing breathing apparatus entered the flat and led two men to safety.
She added: "A 50-year-old man was suffering from severe smoke inhalation and was given oxygen by officers before paramedics took him to Edinburgh Royal Infirmary.
"The other man was checked over but didn't need to go to hospital.
"The fire caused severe damage to the bedroom it started in and smoke damage to the rest of the flat and the central stairs of the building."
The building was checked for damage but other residents in the block did not need to be evacuated, the spokeswoman added.
Firefighters also dealt with a kitchen fire in the capital late on Wednesday night.
A resident of the property in Claverhouse Drive tried to extinguish the blaze before leaving the house to wait for the fire service to arrive.
A neighbour then entered the house to ensure the fire was out.
He was led to safety by firefighters and given treatment for smoke inhalation.
He did not need further medical attention.