The man, said to be in his mid-70s, was taken to the Queen Margaret Hospital in Dunfermline with burns and later died of his injuries.
Police are in the process of contacting his relatives.
The fire started at around 8:40am at Henderson House in Dalgety Bay in Fife.
Three members of staff were also taken to hospital, one man and two women, but only as a precautionary measure.
Fife police are now investigating the cause along with fire investigation teams.
A spokeswoman for Fife Fire and Rescue Service said: “We received a call at 8:40am and three appliances from Dunfermline attended.
“There was a fire in the first floor smoking room of a care home which was extinguished prior to arrival.
“One male casualty suffering burns and three members of staff were taken to hospital.”
A Fife police spokesman said: “A joint investigation with the Fire Service is taking place.
“Police are in the process of contacting relatives.
“No further information will be released until the investigation has been concluded.”
In 2004, 14 elderly people died at Rosepark nursing home in Lanarkshire after a blaze broke out in a cupboard overnight.
A Fatal Accident Inquiry (FAI) heard how dampeners could have stopped the spread of the fire.