Evaluation is presented of the thermogravimetric behavior of four types of rice husk (Lemont, ROK 14, CP 4, and Pa Potho) at three heating rates (10, 20, and 50 degrees C min) in air, oxygen, and nitrogen atmospheres. The thermal degradation rate in active and passive zones, the initial degradation temperature, and the residual weight at 700 degrees C were determined. These thermal degradation indices are dependent on the heating rate, atmosphere employed, inorganic substances in rice husk, and chemical composition of rice husk. The initial degradation temperature decreased, while both the thermal degradation rate and the residual weight at 700 degrees C increased when the heating rate was increased. The higher the cellulosic content of the rice husk, the higher the thermal degradation rate and the initial degradation tempera ture. Also, higher ash content in the rice husk resulted in a higher residual weight at 700 degrees C. The thermal degradation rate in the active zone was higher in the presence of oxygen than in the presence of air and nitrogen. More residual weight was recorded in the nitrogen atmosphere compared to the oxidative atmospheres of the air and oxygen atmospheres. The residual weights of the rice husk samples at 700 degrees C in air and oxygen atmospheres were lower than their initial ash contents, with percentages of ash lost ranging from about 2.95 to 13.10 % in the case of air and 4.20 to 17.05 % in the case of oxygen.