The potential of using molecular approaches to deduce redox conditions in groundwater contaminant plumes was evaluatedin this study. The clone libraries of 16S rRNA gene and the analyses of restriction fragment length polymorphism (RFLP) were appliedto determine the dominant microbial populations in groundwater samples. The results were compared and discussed in the context ofthe redox conditions deduced by dissolved redox-sensitive species. A correlation of the redox conditions with the dominant microbialpopulations in groundwater could be roughly discerned. This study suggests that molecular approaches provide supplementary informationto other approaches, however, so far, using molecular approaches as a sole way to indicate redox processes is not appropriate.