Three people had to be rescued from the burning building by fire crews early on Monday morning.
A 23-year-old man and a 21-year-old woman were rescued from the burning home by fire fighters who took them down a stairwell.
Another 55-year-old man was rescued from the adjacent top floor flat and a 27-year-old man escaped himself.
The fire broke out just before 4am at the flat in Muirhouse Grove in the capital.
Three fire appliances were used to tackle the blaze and one height appliance.
It is not known whether the fire started inside or outside the flat.
All four residents were treated for smoke inhalation and were checked over by ambulance crews but no-one needed to go to hospital.
A spokeswoman for Lothian and Borders Fire and Rescue Service said: “We attended a fire at 3.57am at Muirhouse Grove.
“It was a fire at a doorway in a top floor flat and two occupants were trapped.
“Fire crews rescued the occupants and took them down a stairwell.
“Another male was rescued from an adjacent top floor flat and one further male had self rescued on arrival of the fire brigade.
“Six breathing apparatus and one high pressure hose reel were used and a turntable ladder for assurance.
“Police and a fire investigation team are currently investigating.”
A Lothian and Borders Police spokeswoman confirmed that officers were currently investigating the fire and that it was being treated as “suspicious”.