Isothermal curing of endo-dicyclopentadiene (endo-DCPD) using the first and second generation Grubbs' catalysts as the polymerization initiators was studied by means of differential scanning calorimetry (DSC) according to model-free isoconversional and model-fitting approaches. It revealed that the two Grubbs' catalysts exhibited apparent differences in ring-opening metathesis polymerization (ROMP) of endo-DCPD. The second generation catalyst was more efficient in catalytic activity for overall ROMP of endo-DCPD than the first generation catalyst, as evident from the reaction rate and fractional conversion (alpha). The model-free isoconversional method showed similar dependence of the activation energy (E-alpha) on a for the two catalyst systems; however, the second generation catalyst system involved a higher E-alpha, up to (alpha) approximate to 0.8, above which the E-alpha value suddenly drops with increase of conversion. The model-fitting method of the ROMP was satisfactorily described by the decelerating reaction and the autocatalytic reaction mechanisms for the first and the second generation catalyst systems, respectively. The effect of diffusion-control was incorporated into the model-fitting method to describe the ROMP reaction throughout the entire conversion. For fully cured samples (poly-DCPD), the first generation catalyst system has higher cross-linking density and lower tensile toughness relative to the second generation. Dynamic mechanical behaviors were also different for poly-DCPD formed using the two catalysts.