Police and fire investigators at the scene of the tragedy in Blaxland.
A man has died in the Mountains' third fatal house fire in 48 hours.
Emergency services were called to the Haymet Street, Blaxland, house about 10am Sunday where they discovered the man's body.
The fire, believed to have started in the kitchen, had self-extinguished by the time emergency personnel arrived at the scene.
"Upon arrival they found the house had been involved in a fire, it had actually self-extinguished, and one person had unfortunately deceased as a result of that fire," Fire and Rescue NSW Blue Mountains Zone commander, Acting Superintendent Josh Turner, told media at the scene this afternoon.
"There was a fair amount of smoke and heat damage in the house, located primarily in one part of the house.
"Investigations are under way but it looks like the area that may have been involved is around the kitchen area."
Inspector Paul Glinn from Blue Mountains police said the person who died was believed to be a man aged in his 20s.
"That person is yet to be identified," he told the media.
"This is the third such tragic fatal incident within the Blue Mountains within the last 48 hours, and I guess we'd just like to take this opportunity to remind people to consider the warnings that have been given by NSW Fire abnd Rescue in the last week or so as a result of these types of incidents."
It is the second fatal house fire in Blaxland since Friday, following the death of a man in a duplex on Browns Road.
A woman was also killed in a fire at a Lyons Road, Hazelbrook, home late on Friday. A man and a woman aged in their 70s were rescued from the blaze by officers from Fire and Rescue NSW Lawson and taken to hospital for treatment in serious conditions.