The 67-year-old went missing on Wednesday after setting off on a walk from Agios Nikolaos beach.
The body – which has yet to be formally identified – was found on a hillside near Agia Marina beach bar in the early hours of Sunday.
Symi’s mayor Eleftherios Papakalodouka said the body was found as teams were searching the coastline with cameras.
A police source told BBC News the deceased had been dead “for a number of days”.
The body was found next to a fence, with an umbrella close by, around 30 minutes walk from the village of Pedi where Dr Mosley was last seen.