The fracture mechanics investigation of the dynamically vulcanized EPDM and PP/ionomer ternary blends was performed in terms of the J-integral by measuring fracture energy via the locus method. The ternary blends consisting of EPDM, PP and ionomer were prepared in a laboratory internal mixer by blending and vulcanizing simultaneously. Vulcanization was performed with dicumyl peroxide (DCP) and the composition of EPDM and PP was fixed at 50/50 by weight. Two kinds of poly(ethylene-co-methacrylic acid) (EMA) ionomers were used. The J-integral values at crack initiation, J(c), of the dynamically vulcanized EPDM and PP/EMA ionomer ternary blends were affected by the cation types (Na+ or Zn2+) and contents (5-20 wt%) of the added EMA ionomers. The ternary blend containing 20 wt % zinc-neutralized EMA ionomer and 1.0 p.h.r. DCP showed the highest J(c) values of the blends. The results have been discussed with regard to the fracture topology observed by scanning electron microscopy (SEM).