Abstract: The stress in and elongation of mesophase pitch fibers during oxidative stabilization were investigated by a dynamic thermo-mechanical analyzer under a fixed elongation and strainload,respectively.Their functional groups at different temperatures were characterized by Fourier transformed infrared spectroscopy.Results indicated that when the temperature was below 175℃,a distinct decrease in the stress in the fibers and the number of hydroxyl groups was found,accompanied by dehydrogenation reactions.When the temperature was increased above 250℃,the number of ether bonds and the stress increased,and elongation decreased due to cross-linking reactions.When the temperature was increased further,above 270℃,the fibers began to shrink because of the increase in the extent of stabilization.It was found,based on dynamic thermo-mechanical data,that the effect of gravity on the fiber cannot be neglected in designing a stabilization furnace and a vertical furnace is superior to a horizontal one.