Abstract: An approach was made to quantify the free water content in leaves of Quercus acutissima in different status with differential thermal analysis. The freezing temperatures, peak heights of the exotherms and the areas under the exotherms were clearly observed in the time-domain scanning curve of the differential thermal analysis during cooling, while the larger areas under the exotherms were seen in the temperature-domain scanning curve of the differential thermal analysis, providing a higher sensitivity in quantifying the free water content in the samples. The boundary between the free water and bound water in the tissues was -8.23 ± 0.21 MPa, close to the osmotic potential of a 2 mol*kg^-1 NaCl solution(-8.71MPa). The freeze killed leaves exhibited the freezing feature of a uniform solution with sharp, narrow peaks and higher peak values (1.91 times as that of the living leaves) due to fast temperature rise and fast cooling, while broader peaks with lower values were found in living leaves, indicting a significant retardation of the phase change of water by cell’s membrane system. It is concluded that differential thermal analysis could not only yield the phase change parameters of free water in plant tissues in the freeze-thaw processes, but also quantifying the free water content of plant tissues.