Active fire-induced dynamism of soil humus was found after the analytical comparison of humic polymers from unaltered or burned soil areas, and from laboratory simulated burning on soil samples or soil humus fractions. In general, the polymer structure of humic and fulvic acids were found to be rather resistant to the destruction by fire, but they often underwent noticeable chemical transformation as revealed by physical and chemical methods. The most significant alterations arose from the selective destruction of specific oxygen containing functional groups, which probably contributed to a condensation of the tertiary structure of the humus polymers. These effects were responsible for the transformation of fulvic acid into humic acid like polymers. To all appearances, the modifications observed in the properties of the humic polymers are responsible for the changes in aggregation, wettability, mobilisation of cations, acid for the biological activity of the soils under burned areas.