The rheological behavior of a reactive blend system of nylon1212 with maleic anhydride grafted poly(ethylene-octene) was studied in correlating with the key mechanical parameters. Results illustrated that the "gel points" acquired from the dynamic theological data and the "super-toughness points" of the blends have a corresponding relationship. Thus, just by simple composition designs and a small amount of samples, the super-toughness point could be conveniently determined by the dynamic rheological measurements. Furthermore, special "double network" morphology at the gel point was directly observed for the first time and the new mechanism of super-toughness has also been discussed. (C) 2015 The Society of Rheology.