Thermal analysis, TGA and DTA, of the bagasse kraft black liquor was carried out under an oxidized atmosphere (combustion) and an inert atmosphere (pyrolysis). It was found that dried black liquor evaporated and pyrolyzed over a broad range with considerable loss between 70 and 800degrees C. There are indications of peak activity at 50, 273, and 630degrees C under oxidizing atmosphere and 70, 292, and 637degrees C under inert atmosphere. The activity at lower temperatures is most likely due to volatilization of organic and breakdown of sulfur compounds. The activity at higher temperatures is probably due principally to pyrolysis of organic. During pyrolysis an additional, final, step covers a temperature range of 800 to 1000degrees C; this is due to fusion of inorganic sodium salt. During combustion of dried black liquor, the oxidation condition is favorable at the beginning of the combustion operation, while the reducing condition is favorable at the end.