The incident happened on Green Hill Road in Armley, with firefighters being called shortly after 12.20am.
Two men, one aged around 60 and the other around 40, were suffering from the effects of smoke inhalation.
One of the men was given a precautionary check-up at the scene while the other went to hospital by ambulance.
The fire affected the living room of the property, which was fitted with working smoke detectors.
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Crews from Stanningley and Leeds fire stations attended the incident.