Studies of soil organic matter (SOM) characterization are used to assess soil fertility and sustainability. The present research characterized the soil organic matter under various forest types: dense ombrophilous forest, “campinarana florestada”, “campinarana arbóreo-arbustiva”, “campinarana gramíneo-lenhosa” , and pioneer formations. Soil analyses aimed to characterize and quantify total organic carbon (TOC) and total nitrogen (TN) of soils and organic carbon (OC) of humic fractions. Methods used included bichromatometry for TOC determination ; TN - Kjeldahl method, and OC of the humic fractions – bichromatometry. Other analisys included CEC and granulometry determination. The soils generally revealed low fertility. The soils under “campinarana florestada” presented the highest CEC and TOC revealing a correlation between CEC and SOM in this sandy soil. Humic fractions in the “campinarana florestada” showed humin > humic acid > fluvic acid. This was due to limited SOM degradation, resulting from presence of rich polyphenolic compounds and higher lignified material. The other phytophysiognomies studied presented a predominance of humin fraction over the fulvic acids. In the pioneer formation, “campinarana gramíneo-lenhosa” and “campinarana arbórea-arbustiva” the predominance of fulvic acids over the humic acids results from the presence of grassy strata material which is easily decomposed due to atmospheric conditions which allows an intense SOM oxidation. The loss of humic substances in the soils under this vegetation is associated with the presence of dark-colored water which is rich in these substances that are drained in those sites. The prevalence of humic acids in “campinarana florestada” is associated with the increasing root development of the present vegetation, which assures lower nutrient losses in the vegetations; therefore it assures the sustainability of their ecosystems. Key words: Carbon, Humic substances, Campinarana, white-sand vegetation, entisol.