Police and paramedics were called to the terraced home in Southfleet Avenue following a 999 call at around 9.50pm.
They found a woman in her 40s who had suffered serious head injuries and she was taken by ambulance to Royal Preston Hospital.
A 25-year-old man, from Fleetwood, was arrested on suspicion of assault and remains in custody this afternoon.
A police spokesman said: “We were called around 9.50pm yesterday (Wednesday, May 4) to a report of an assault at an address in Southfleet Avenue, Fleetwood.
“Emergency services attended with a woman aged in her 40s found with serious head injuries.
“She was later taken to Royal Preston Hospital for treatment.
“A 25-year-old man from Fleetwood was arrested on suspicion of assault and is in custody.”
North West Ambulance Service has been approached for further details on the woman’s condition.