This paper describes the application of dynamic microcalorimetry to determine the thermokinetics of short-time enzymatic reactions. A thermokinetic double-parameter method for faster enzyme-catalyzed reactions is proposed on the basis of the double-parameter theoretical model of the conduction calorimeter. By analyzing the calorimetric curves of faster enzyme-catalyzed reactions, this method can be conveniently used to calculate both molar reaction enthalpy ( Δ r H m) and kinetic parameters ( K m, ν max) of these reactions. Thermokinetics of the oxidation of xanthine catalyzed by xanthine oxidase in the presence of excess oxygen has been studied using microcalorimetry. This faster enzyme-catalyzed reaction obeyed the Michaelis–Menten kinetics, and the Michaelis constant ( K m) for xanthine and the overall molar reaction enthalpy ( Δ r H m) of this oxidation were determined by this method to be 1.04×10 −3 mol dm −3 and −5.25 kJ mol −1, respectively, at 298.15 K and pH 7.5. The reliability of the double-parameter method for faster enzyme-catalyzed reactions was verified by the experimental results.