Lead carbonate, doped with 0.1–10 mol-% strontium, was mechanically activated by vibro-milling. The excess enthalpy, Δ H ∗, imparted to the activated materials, remained almost constant, irrespective of the strontium concentration. The first-order rate constant of isothermal decomposition, k p0, of the doped materials without mechanical activation decreased only slightly with increasing concentration of strontium. For the mechanically activated materials, however, k p significantly decreased with increasing concentration of strontium. A quasi-linear relationship was found between the apparent activation energy, E a, and the logarithm of the pre-exponential factor, 1n A, of decomposition. This enabled the characteristic temperature, T x , to be determined for each group of samples with different strontium concentrations. At T = T x , the excess free energy was assumed to become null. From the relationship between T x and the decomposition temperature. T D, determined from the differential scanning calorimetric profile, the extent of excess free energy dissipated during the decomposition reaction is suggested to decrease due to strontium doping.