Firefighters from across Southampton were called to a ground-floor flat fire on Bullar Road at 11:38 on Friday (3 Dec).
The body of the woman was found in a ground-floor flat and she was confirmed dead at the scene.
Crews from St Mary’s, Hightown and Eastleigh fire stations were able to rescue one casualty from a first-floor flat, before extinguishing the fire using six sets of breathing apparatus, three hose reels, jets and ventilation fans to clear smoke.
South Central Ambulance Service paramedics treated one casualty for smoke inhalation who was then taken onto hospital, as Hampshire Constabulary officers implemented a road closure.
The flat suffered severe damage from the fire and smoke, with neighbouring flats also affected by the smoke.
HIWFRS crews remained on the scene following the stop message at 13:09, before fire investigation officers attended.