Abstract: The structures and properties of the composite films formed by soy protein isolate (SPI) and xanthan gum (XG) with different other matrices were investigated. The composite films were prepared with SPI and XG by adding sodium alginate (SA), carboxymethyl cellulose (CMC), gelatin (GEL), pectin (PEC) and agar (Agar), respectively. The thickness, mechanical properties, oxygen permeability and opacity of the composite films were measured, and their structures were characterized. The results showed that the thicknesses of composite films with 1.5 g of different other matrices were significantly higher (P<0.05) than the film of SPI/XG, and the maximum tensile strength was 5.90±0.32 MPa for SPI/XG-Agar film (P<0.05), the oxygen permeabilities of them were significantly reduced (P<0.05), and the lowest opacity was 0.45±0.09 Abs₆₀₀/mm for SPI/XG-Agar film (P<0.05). The photograph of SEM showed that the surface of SPI/XG-Agar composite film was flat, smooth and free of particles, while the other composite films were with particles and folds on the surface. The infrared spectroscopy analysis showed that there was good compatibility between all the matrices. The results of tensile strength, opacity and SEM for the SPI/XG-Agar film were superior to other films.