Police were called to the property in Mayfield Crescent, Worsbrough, at around 9.40am.
They were met by ambulance staff and a 30-year-old's body had been found.
A South Yorkshire Police spokesman said: "At this time, the cause of death is not known and a forensic post-mortem is expected to be carried out later this evening.
"A 27-year-old woman who was also at the property has been arrested on suspicion of murder and currently remains in police custody."
Anyone with information is asked to call 101.