They were alerted to check the room and found the body of Chananthida Noo-iad, 41, with bruises around her neck, covered by a sheet on her bed.
Pol Lt-Colonel Thirdthai Sukthai, deputy commander of Muang Suphan Buri station, said the woman apparently died at least 20 hours before police found the body.
She worked a construction contractor and had been renting the room since June 21.
The woman, who was divorced, was believed to have had a relationship with a man known only as Pong.
Other tenants of the apartment building told police that they heard a loud noise from the room on Monday night.
A sister of Chananthida's ex-husband said she talked to the woman at 10pm on Monday but had been unable to contact her since.
Her body was sent for an autopsy.