Police were called to Wellington Street in Greenock, Inverclyde at 1.15am.
A 29-year-old man was found seriously injured at the address by officers. He was taken to hospital but later died.
A police spokeswoman said: "On arrival, police found a man seriously injured. A 29-year-old was taken to Inverclyde Royal Hospital where he later died.
"A murder investigation is under way."
Police have asked anyone with information about the incident to contact CID at Greenock police office or by calling 101.