Sugar cane fiber (i.e., bagasse) is the residue from sugar cane milling during sugar manufacture. This study uses chemical analysis, thermogravimetry analysis (TG), derivative thermogravimetry (DTG), X-ray powder diffraction (XRD), and energy-dispersive spectroscopy to investigate the composition and thermal decomposition of bagasse from various origins. The results indicate that bagasse from different varieties of sugar cane have different proportions of carbohydrates, lignin, and ash contents and different degrees of crystallinity. TG thermograms show four distinct stages of mass losses instead of three stages reported for bagasse decomposition. This is due to the presence of residual sucrose. The thermal decomposition profile of bagasse is independent of origin, though minor differences exist in the temperatures at the maximum rate of weight losses for the hemicellulose and cellulose components of bagasse as well as on the residue yield. The main phases in ashes of the bagasse chars are quartz, acranite, and langbeinite, with slight shifts in the d values among the samples probably related to differences in the concentrations of inorganic ions in the crystal lattices. The results are further discussed in terms of the activation energy of the devolatilization process obtained using Friedman's method.