The mechanical properties and fracture behavior of natural rubber/poly(methyl methacrylate) blends were investigated as a function of composition, graft copolymer concentration, and mixing conditions. The mechanical properties and failure behavior vary with the blend ratio, graft copolymer concentration, and mixing conditions. Various two-phase models were used to fit the experimental mechanical properties. Mechanical properties such as stress-strain behavior, tensile strength, tensile modulus, tear strength, and Izod impact strength were evaluated asa function of compatibilizer concentration. The domain size of the dispersed phase decreases with graft copolymer concentration followed by a leveling off at higher concentration. The mechanical properties attain a maximum value at the leveling point, which is an indication of interfacial saturation and the attainment of maximum interfacial adhesion between the homopolymers. Tensile and tear fracture surfaces were examined by scanning electron microscopy. The detachment of the dispersed domains from the matrix is an indication of no adhesion between the two phases in the case of uncompatibilized blends. Microfibrils between the matrix and the dispersed phase indicate a sign of interfacial adhesion between the phases in the case of compatibilized blends.