The present invention relates to a soybean-based adhesive resin including a soybean flour and a cross-linking agent. The cross-linking agent is reacted with the functional groups in the soybean flour to form an adhesive resin. The present invention also relates to a method of making a soybeanbased adhesive resin. This method involves providing an aqueous solution of soybean flour and adding a cross-linking agent to the solution under conditions effective to cross-link the soybean flour so that an adhesive resin is formed. Also disclosed is a composite product which includes particulate plant material and the soybean-based adhesive resin. The adhesive is prepared by reacting the cross-linking agent with the functional groups in the soybean flour. The present invention also relates to a method of making a composite product by providing particulate plant material and applying the soybean-based adhesive resin to the particulate plant material.