Sulfur (S) is an essential nutrient for all organims including plants. The range of biological compounds that contain S is vast. In particular, S has important structural and catalytic functions for proteins. Since several years, S deficiency has been recognized as a limiting factor for crop production especially for rape. The insufficient S supply reported, which can affect the yield and quality of the crop, is essentially due to a drastic reduction of S dioxide emissions in the atmosphere. Therefore, sulfate is now the primary source of S for plants which take it up from the rhizosphere. However, in soil, more than 95% of S is organic bonded. Then, the mineralization of these organic S forms via microbial processes may contribute to the S supply of plants. Until now, arylsufatase (ARS) has been considered as a key enzyme implicated in the hydrolysis of ester sulfates, the most labile form of soil organic S. Genes encoding ARS can be used as molecular markers to characterize sulfur mineralizing communities which are still weakly described. The objective of this work was to analyse the evolution of the potential ARS activity in relation with changes in the genetic structure of the functional fungal community in the rhizosphere soil of field-grown plants. The analysis was done along the phenology of rape and barley ; two species with contrasting S requirement. For that, a taxonomic identification of S- mineralizing fungi based on 18S rDNA sequences was carried out after isolation onto a specific agar medium containing a synthetic ester sulfate as a unique source of S. We observed a higher potential ARS activity in the rhizosphere soil of rape as compared to the barley rhizosphere soil and this ARS activity exhibited temporal variations. Our first results concerning taxonomic characterisation of S mineralizing fungi showed the implication of several genera belonging to Ascomycota. Differences in the relative abundance of the identified ribotypes were observed between rape and barley rhizosphere soil. This work gives a first insight of the role of fungi in S mineralization.