In this work the thermal analysis of raw and defatted sisal fiber and its chemical constituents (cellulose, hemicellulose and lignin) was performed by thermogravimetric analysis, and differential scanning calorimetry under air and nitrogen atmospheres. The DSC studies showed that the degradation process depends on the atmosphere involved. In inert atmosphere, the DSC curves exhibited distinct peaks for sisal fiber and its constituents, whereas in air atmosphere the thermal curves presented two exothermic peaks for all the constituents. The degradation of cellulose in inert atmosphere occurred by endothermic processes whereas, in air atmosphere, it occurred by exothermic processes. TGA measurements corroborated the results obtained by DSC. It is shown that cellulose and hemicellulose degraded at lower temperatures than that of the raw sisal fiber, which can be attributed to the removal of lignin. The thermal decomposition of sisal fiber and its constituents was discussed and compared to jute and hemp fibers. (C) 2010 Published by Elsevier B.V.