This article reports the synthesis and characterization of a novel biodegradable plastic synthesized from the serum albumin of bovine blood (BSA) by using the sub-critical water technology in batch reactors. The optimum synthesis conditions were found to be in the range of 250-275 degrees C for a reaction time of 1 min using 160 g/L BSA as an initial concentration. After a reaction time of only 0.5 min, all water-soluble BSA molecules were completely transformed into water-insoluble solids without hydrolysis or decomposition. A variety of techniques have been used to study the nature of the formed solids. The obtained results reveled that such solids showed many plastic properties and could be processed to produce a biodegradable plastic. The produced solids were recovered, dried, and thermally processed to produce a plastic BSA (PBSA). In this way, it was possible to obtain a material with a variety of mechanical properties that might allow for its application in both the biomedical as well as the traditional biodegradable plastic fields. The average values of the yield strength and modulus of elasticity of the processed samples synthesized at 250 degrees C for 1-min reaction time were 31.2 and 780 MPa, respectively. The biodegradability was confirmed by measuring the methane gas production and weight losses during an anaerobic fermentation of the processed plastic samples. (c) 2006 American Institute of Chemical Engineers.