The woman told officers she contacted a man in response to an online ad for the flat in the city of Malmo. She said the landlord told her he expected her to perform sex acts both before and after she got the apartment.
The woman declined to meet the landlord and instead reported the matter to police, TheLocal.se reported Saturday.
Officials have classified the incident as sexual molestation and blackmail, though it was unclear whether the landlord had been arrested.
Detectives urged other women who may have inquired about the apartment to come forward if they were approached by the landlord in a similar manner.