Humic acids are considered problematically in drinking water because it can react readily with chlorine to form carcinogen compounds and its biological removal is much recommended. The scanning electron microscopy morphologies and optical parameters observed for natural humic acids (NHAs) extracted from different soils at Mitidja plain (Algeria) made them different from the commercial ones. Three of the most active strains 01 19 actinomycetes were isolated and selected from surface soils at this plain. These strains were identified based on cultural characteristics and chemotaxonomic analysis and classified in the genus Streptomyces. Growth of these strains was assured on a poor liquid medium containing NHAs as carbon and nitrogen sources and degradation occur only in the presence of glucose. A maximal decolorization extent was obtained for 28 days at 30 degrees C under shake culture (67%, 66% and 57% for Streptomyces sp. strain AB1, Streptomyces sp. strain AM2 and Streptomyces sp. strain AH4, respectively). As compared with initial and final structures of NHAs after incubation (28 days), the structural changes in FTIR spectrum and metabolite products analyzed by HPLC indicate the capability of the selected Streptomyces sp. strains to degrade HAs and to play a part role in humus turnover in natural waters. (C) 2010 Elsevier B.V. All rights reserved.