Two kinds of transparent films of soy protein were successfully prepared by plasticizing with diethanolamine (DEA) and triethanolanun (TEA). The films were hot pressed at 140 C and 20 MPa, and characterized with Fourier transform infrared spectroscopy, scanning electron microscope, ultraviolet-visible spectrometer, differential scanning calorimetry (DSC), thermogravimetric analysis, and tensile testing. The results indicated that films with triethanolamine plasticizers possessed better optical transmittance (more than 80% at 800 nm) than those with diethanolamine and glycerol. All of the sheets exhibited only one T-S in DSC curves. Moreover, the soy protein plastics with TEA had higher thermal stability and mechanical properties, as well as lower water uptake than those with DEA and glycerol, as a result of the strong interaction between TEA and protein molecules. The soy protein materials will be promising for the application in the fields of package and container, substituting for the nongreen polymers. (c) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 117: 1549-1556, 2009