Conductive soy protein biocomposite plastics with high performance were fabricated with glycerol as plasticizer and nanosized carbon black (CB) as conductive filler. Adopting a pretreatment of the CB nanofiller, its dispersion, and interaction with matrix was improved. The results indicated the existence of strong hydrogen bonding between soy protein matrix and CB fillers, which improved the interfacial bonding. The strong interactions between CB and protein restricted the mobility of protein segments, resulting in a dramatical reinforcing effect for the CB filled composites and enhanced mechanical properties. Besides, the incorporation of CB into soy protein increased the thermal stability as well as the water resistance of the composites. Moreover, a low percolation threshold of 0.76 vol% and fine electrical conductivity were In order to protect the environment from plastic pollution and realizing the depletion of oil resources, the attention of the researchers is ever increasing to make composites and nanocomposites from natural polymers with low cost and biodegradable properties. 1-3 Soy protein is a biopolymer derived as a byproduct from soy seeds processing. Soy protein possesses fine biocompatibility, biodegradability, functional side chains, adjustable structures, and certain processability. 4 This nonbioactive protein has gained increasing attention in material science in recent years, which could be fabricated into films, fibers, foams, and applied in various fields, such as, packaging, coatings, air filtration, and so forth. 1,5,6