Self-healing soy protein isolate (SPI)-based "green" thermoset resin is developed using poly(D,L -lactide-co -glycolide)(PLGA) microcapsules containing SPI, as crack healant. The SPI-PLGA microcapsules with an average diameter of 778 nm that contain sub-capsules are prepared using a water-in-oil-in-water double-emulsion solvent evaporation technique. The encapsulation efficiency is found to be high, up to 89%. Thermoset green SPI resin containing the SPI-PLGA microcapsules successfully arrests and retards the microcracks. The healing efficiency is investigated using mode I fracture toughness test for resins containing different concentrations of microcapsules from 5 to 20 wt% and glutaraldehyde as a crosslinker at 9 or 12 wt%. The SPI resin containing 12 wt% glutaraldehyde and 15 wt% microcapsules shows self-healing efficiency of up to 48%. It is observed that the SPI released from SPI-PLGA microcapsules can react with the excess glutaraldehyde present in the resin when the two come in contact within the microcracks and bridge the two fracture surfaces. The results of this study show for the first time that SPI-PLGA microcapsules can self-heal protein-based green resins. The same method can be extended to self-heal other proteins as well as protein-based green composites resulting in higher fracture toughness and longer useful life.