Although the thermodynamic quantities are very fundamental and important quantities to describe chemical states, these quantities have been studied only under the equilibrium condition. This limitation was a serious problem for understanding transient chemical processes including photochemical reactions. One challenge facing chemists studying chemical reactions is to obtain thermodynamic information about non-equilibrium states involved in rapid reactions. Several methods we have developed recently for the measurement of the time-resolved thermodynamic quantities were reviewed. Using these methods, we are now able to measure the initial step of the heating process due to the nonradiative transition, enthalpy of reaction, partial molar volume change, thermal expansion coefficient, and heat capacity of transient species.