Quantifying past oxygen concentrations in oceans is crucial to improving understanding of current global ocean deoxygenation. Here, we use a record of pore density of the epibenthic foraminifer Planulina limbata from the Peruvian Oxygen Minimum Zone to reconstruct oxygen concentrations in bottom waters from the Last Glacial Maximum to the Late Holocene at 17.5°S about 500 meters below the sea surface. We found that oxygen levels were 40% lower during the Last Glacial Maximum than during the Late Holocene (about 6.7 versus 11.1 µmol/kg, respectively). A comparison with other reconstructions of oxygen concentrations in the region reveals a shallow Oxygen Minimum Zone during the Last Glacial Maximum that was similar in water depth and extent but weaker than during the Late Holocene. Increased glacial oxygen concentrations are probably related to lower temperatures (higher oxygen solubility), decreased nutrient and increased oxygen supply by source waters, and a decrease in coastal upwelling.