The morphology of double oxide film defects and their influence on the tensile mechanical properties of a commercial Cu–Al(C95800) alloy were investigated in this study. Plane castings were produced with two types of pouring systems, and their tensile properties were measured and then analyzed by means of Weibull statistics method. The fracture surfaces of the tensile specimens were examined using scanning electron microscopy equipped with energy-dispersive spectroscopy. A large amount of double oxide film defects were observed on the tensile fractured specimens of the topfilled plane castings, and their chemical composition is identified to be Al_2O_3. Weibull statistics analyses showed that the double oxide film defects significantly reduce mechanical properties of the castings investigated. Furthermore, the ultimate tensile strength is more obviously deteriorated by double oxide film defects than elongation. The morphology of double oxide film defects and their influence on the tensile mechanical properties of a commercial Cu-Al (C95800) alloy were investigated in this study. Plane castings were produced with two types of pouring systems, and their tensile properties were measured and then analyzed by means of Weibull statistics method. The fracture surfaces of the tensile specimens were examined using scanning electron microscopy equipped with energy-dispersive spectroscopy. A large amount of double oxide film defects were observed on the tensile fractured specimens of the topfilled plane castings, and Their chemical composition was identified to be Al 2 O 3. Weibull statistics analyzes showed that the double oxide film defects significantly reduce mechanical properties of the castings investigated. Furthermore, the ultimate tensile strength is more obviously deteriorated by double oxide film defects than elongation.