Some properties of soil organic matter (SOM) in Vertisols were studied in four profiles from the South, Central and North Gezira of Sudan using Thermogravimetry. The characteristics examined include the dynamics of weight loss, content of biodegradable and humified components of SOM and the proportions of these components in total organic matter. Differences were found between these components in relation to location of profile and horizon studied. The highest amounts of biodegradable components of SOM were found in South Gezira soil where both the clay content and the annual rainfall are highest with a systematic decrease northwards. A close positive correlation was found between the content of humified SOM and the clay content in soils. Comparing the continuously cropped sites with the permanent uncultivated non-cropped ones reveals that long termo-irrigation and continuous cropping has affected the quality of SOM in the soils studied.