Biodegradable plastics (GSD) based on soy dreg (SD) were prepared by compression-molding, with glycerol as the plasticizer and glutaraldehyde (GA) as the cross-linker. The structure and properties of the GSD sheets were investigated by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), scanning electron microscope (SEM), and tensile test methods. The results indicate that when GA content was 6.8%, the tensile strength (sigma(b)) of the sheet reached the maximum value of 14.5 MPa. Moreover, the strength and water resistance of the sheets coated with castor-oil-based polyurethane/nitrochitosan interpenetrating network (IPN) coating were significantly enhanced to 24.6 MPa in the dry state and 9.8 MPa in the wet state. Simultaneously, the test of biodegradability of the GSD sheet in a mineral salts medium containing microorganisms and agar proved that GSD could be fully biodegradable. This work has provided a novel way to utilize low-cost SD to prepare biodegradable plastics. (C) 2003 Wiley Periodicals, Inc.