Earlier we reported emergency services were called to an address on Albert Avenue, Skegness, at around 6.50pm on Thursday.
The woman was pronounced dead at the scene and her family were made aware.
Police said they were not treating the death as suspicious and a file was being prepared for the coroner as investigations continued..
A spokesperson for Lincolnshire Fire and Rescue told Lincolnshire Fire and Rescue the cause of the fire had now been determined.
The spokesperson said: “The findings of the fire investigation determined the cause to be accidental and attributed to smoking materials in bed.”