Reconstruction of the Mediterranean Outflow Water (MOW) dynamics in the geologic past contributes to exploring its influence on the North Atlantic Ocean circulation and the climate. The middle Pleistocene transition (MPT) is one of the most important characteristics of Quaternary climate change, but until now, research on the MOW variability during this time interval has been limited. This work presents the first continuous and high-resolution (~2 kyr) foraminiferal stable oxygen and carbon isotopes and benthic foraminiferal records from Integrated Ocean Drilling Program (IODP) Site U1391, drilled off the Portuguese margin in the Northeast Atlantic Ocean, to decipher the MOW variability over the last 1.3 myr.