In this work, the mechanical performances of poly (methyl methacrylate)-modified starch/styrene-butadiene rubber (PMMA-modified starch/SBR) biocomposites treated by several coupling agents, i.e., bis(3-triethoxysilyl propyl)tetrasulfide (TESPT), 3-aminopropyl triethoxysilane (APTES), 3-Mercaptopropyl triethoxysilane (MPTES) and 4,4-methylene bis (phenyl isocyanate) (MDI), were investigated. The measurements of resulted biocomposites demonstrated that the biocomposites treated by MDI exhibited the superior reinforcement, in which the tensile strength and 300% modulus were increased up to 11.8 and 7.5 MPa, respectively. The strong chemical bonding in the PMMA-modified starch/SBR interfaces resulted from MDI intermediated linkages was responsible for this observed reinforcement. Furthermore, the enhanced interfacial interaction was confirmed via the changes in the morphology, storage modulus, glass temperature and initial decomposition temperature.