The heat denaturation of the rice mitochondrial DNA in two different media has been studied by using ultraviolet absorption spectrometry er the temperature range 25-85 degrees C. The heat denaturation curve of the rice mitochondrial DNA in 0.15 mol.L-1 NaCl solution has been obtained and the thermodynamic functions of the rice mitochondrial DNA in the heat denaturation process have been calculated. Furthermore, the relationship between these thermodynamic functions and the structure of the rice mitochondrial DNA has been discussed preliminarily.