The thermal behavior of grass fiber was characterized by means of thermogravimetric analysis and differential scanning calorimetry analysis. The results proved that the removal of water-soluble matter improved the thermal behavior of grass fiber over that of unleached fiber, and this was further enhanced by an alkali treatment of the grass fiber. The isothermal weight loss of the grass-fiber specimens was analyzed at 100, 200, and 300 degrees C for different time periods. Accelerated aging of the grass-fiber samples was carried out to determine the effect of aging on the tensile strength. Partially delignified grass fiber showed maximum thermal stability. X-ray diffraction analysis was also performed to verify the composition and to correlate the change in the tensile strength due to the water leaching and alkali treatment. The processing of grass fiber with NaOH and NaClO2 reduced the amorphous fraction in the fiber sample. This may have been a result of the loss of the amorphous noncellulosic components of the fibers and the degradation of the unordered regions of the grass fiber. However, mercerization of the grass fiber revealed an increase in the amorphous fraction after a certain time exposure, confirming the decrease in the crystallinity. The morphology of the water-leached and alkali-treated grass fiber was studied with scanning electron microscopy (c) 2008 Wiley Periodicals, Inc.