Elemental. functional and spectroscopic analyses (FTIR, C-13-NMR) were performed to study fulvic acids of composted olive mill wastes plus cereal straw, in order to follow the maturity of the final product during composting. The extracted fulvic acids were characterized by hi h nitrogen, acidic functional group and phenolic hydroxyl contents that might have resulted from the high degree of hurnification and the synthesis of more condensed humic complexes. This was confirmed by a decrease of alcoholic and aliphatic structures and an increase of aromatic structures, as shown by the FTIR and C-13-NMR analyses. The results showed that stability of the final product was reached after 12 months of composting and that fulvic acid levels could constitute an additional tool to assess final product maturity and its agronomic value. (C) 2003 Elsevier Ltd. All rights reserved.