Isoxaflutole is an herbicide activated in soils and plants to its diketonitrile derivative, the2 active herbicide principle. Then, the diketonitrile derivative undergoes cleavage to the inactive benzoic acid analog. In this paper, we establish that an oxidative mechanism implicating two successive reactions in the presence of dimethyldioxirane can chemically initiate the cleavage of the diketonitrile. We also show that two white rot strains,Phanerochaete chrysosporium and Trametes versicolor, are able to convert the diketonitrile to the acid, when cultured in liquid media. This main metabolite amounts to 24.6 and 15.1% of initial herbicide content after 12-15 days of culture. Another polar metabolite represents less than 3.7% of parent compound amount during the same period. Oxidative enzymes produced by the fungi show a similar time course to diketonitrile degradation. Purified laccase (EC 1.10.3.2), in the presence of 2 mM 2,2’-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) acting as a redox mediator at pH3, supports the reaction with rates of 0.3-0.4 nmol h-1 U-1.