¹⁵N DNA stable isotope probing was used to identify microorganisms responsible for degradation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) from soil microcosms. An agricultural soil was amended with either unlabeled or labeled (¹³C₃¹⁵N₃) RDX along with added mineral salts medium and glucose. Following RDX degradation monitored through HPLC analysis, DNA was extracted from both sets of microcosms. The DNA samples were then subject to isopycnic density gradient ultracentrifugation, fractionation, followed by terminal restriction fragment length polymorphism on 'heavy' fractions. One fragment was dominant in heavy fractions of ¹³C ¹⁵N-RDX amended samples, but not in the unlabeled controls indicating label uptake by this organism from RDX. Sequencing of the total DNA indicated the organisms involved in RDX transformation belonged to the class of Sphingobacteria and Acidobacteria . These organisms have not been associated with RDX degradation so far, but have been noted for their ability to degrade many other xenobiotic compounds such as MTBE, BTEX, tetracyclines and PCBs. This study indicates the potential for identifying more non-indigenous RDX degrading microorganism from uncontaminated soils.