Crews from Dee Road and Caversham Road were called to the Oxford Road flat, near the junction with Grovelands Road, at 4pm and pulled the woman, in her 60s, to safety.
Watch manager Luke Coleman said: "As we arrived, we were flagged down by a neighbour from the ground floor flat telling us that the occupant was still in the property.
"We arrived before the paramedics, but we were able to get her out of the flat and down the stairs to the ground floor, where we kept her out of the gaze of passers-by."
The woman was taken to Royal Berkshire Hospital to be treated for severe smoke inhalation while fire crews spent two hours battling the flames, which caused extensive damage to one room and smoke damage to the entire flat.
The cause of the fire is being investigated.