Blending of high-density polyethylene (HDPE), natural rubber (NR) and thermoplastic tapioca starch (TPS) has been studied. The composition of HDPE/NR was fixed at blend ratio of 70/30. Three series having 5–30% TPS content were prepared for (a) unvulcanized blends, (b) sulfur vulcanized HDPE/NR/TPS blends and (c) N,N′-m-phenylenebismaleimide (HVA-2) vulcanized HDPE/NR/TPS blends. Tensile strength, Young's modulus and elongation at break exhibit significant improvement when HDPE/NR/TPS blends were subjected to HVA-2 crosslinker when compared to unvulcanized counterparts. SEM micrographs show fine TPS dispersion and well embedded in vulcanized HDPR/NR matrix. Comparison was also made based on the results of gel content, thermogravimetric analysis (TGA) and differential scanning calorymetric (DSC). The improvement observed in tensile properties, thermal stability and blend morphology can be correlated to the crosslink formation within the NR phase.