Abstract: To enhance the oxidation resistance of ultra-thin electrolytic copper foil, aluminum sulfate additives with varying concentrations were added to the electrolyte, and their impact on the structure and oxidation resistance of the ultra-thin electrolytic copper foil were investigated. The mechanism by which aluminum sulfate improves oxidation resistance was investigated through a series of characterization tests, including X-ray diffraction spectroscopy, transmission electron microscopy, inductively coupled plasma chromatography-mass spectrometry, electrochemical testing, field emission scanning electron microscope, and electron backscatter diffraction. The results show that adding aluminum sulfate can effectively improve the oxidation resistance of ultra-thin electrolytic copper, with the optimal performance achieved at an aluminum sulfate additive concentration of 30 mg/L. This improvement is attributed to the addition of aluminum sulfate, which lowers the electrodeposition overpotential of copper ions, promotes the electrodeposition reaction of copper ions, increases the number of copper particles within the copper foil, homogenizes the grain size, and facilitates the formation of a significant number of twin crystals. At the same time, Al³⁺ can co-deposit with Cu²⁺. It may exist in the ultra-thin electrolytic copper foil in the form of an alloy, thus improving the oxidation resistance of ultra-thin electrolytic copper foil. This work presents novel ideas for enhancing the antioxidant properties of ultra-thin electrolytic copper foil.