The body of a 42-year-old from Preston was found at an address on Church Street in the city centre at about 20:30 BST on Tuesday, police said.
Paramedics were called and he was pronounced dead at the scene.
A 37-year-old man, who was arrested in connection with the death, is currently in police custody.
A man has been arrested on suspicion of murder following the "unexplained" death of a man in Lancashire.