West Sussex Fire and Rescue said crews were called to a "ferocious fire" in the kitchen of the property in Harwood Road, Littlehampton, at 12:10 BST.
Police said a woman inside the house died, while two other adults were taken to hospital suffering from the effects of smoke inhalation.
The cause of the fire is currently being treated as unexplained.
Anyone who saw what happened at the time the fire broke out or who may have any other information is asked to contact Sussex Police.
A woman has died and two other people have been injured following a fire at a terraced house in West Sussex.