Fusarium graminearum causes wheat head blight disease and produce different mycotoxins (as Deoxynivalenol=DON) which are toxic for human and animal. During off season it survives in the soil, on weeds and in crop residues. A 6 months study was conducted in controlled conditions (microcosms of natural soil, 17°C, 80%WHC) to test whether the presence of DON in the wheat crop residues gives advantages to F. graminearum to survive and develop a primary inoculum during the decomposition process. This study was carried out in the presence of the whole soil biota (i.e. fungi, bacteria, protozoa, nematodes and earthworms). Both F. graminearum and the biota were monitored during the decomposition process. The wheat crop residues were placed on the soil surface or incorporated into the natural soil. This experiment was conducted with (1mg DON/kg soil-straw mixture) and without DON. This study suggested that the mycotoxins provided a competitive advantage to F. graminearum and were deleterious towards the fungal community and the nematodes but not towards the bacteria or the earthworms. However, all the results were not statistically significant. The use of molecular tools as well as the forthcoming quantification of DON in the residues during 24 weeks of observation will provide the clarification and may confirm or not the trends we observed.