The fire broke out in Björklinge, 20km north of Uppsala.
“The woman in the family knew that the man had gone to the outside toilet,” police spokeswoman Elle Gustafsson said.
“She saw smoke and fire from the toilet hut and called the fire brigade,” she added.
The outhouse was completely ablaze by the time the police arrived on the scene at 6.12am.
A body, believed to be that of the man, was found in the hut. Police are to carry out a forensic examination of the scene to discover the cause of the fire.