Novel blend films of soy protein isolate (SPI) and poly(vinyl alcohol) (PVA) compatibilized by glycerol were fabricated by preparing a solution, and then casting it on a Teflon-coated metal sheet. Mechanical, biodegradation and water vapor permeability of the blend properties were systematically investigated with various methods. SEM analysis results release that the SPI/PVA/glycerol film degrades at a slower rate than pure SPI. The mechanical test showed that the stress at yield point, stress at break point and Young's modulus were decreased and percentage elongation at yield point and percentage elongation at break point and of SPI/PVA were increased obviously than pure SPI films. The blend plastics were softened and became semi-rigid contributing to the plasticization of glycerol and the crystalline partion of PVA was destroyed by glycerol. Water vapor permeability of SPI/PVA/glycerol showed the minimum at the component of SPI/PVA (100/35) compatibilized by 3.5% of glycerol.