Microbial communities can dominate Fluid Fine Tailings (FFT) in the presence of electron acceptors (e.g. Sulfate). Sulfate reduction can produce hydrogen sulfide, one of several chemical constituents responsible for sediment oxygen demand (SOD). The preservation of RNA is a crucial step to study active microbial populations and their activity in FFT and hence understand the biological factors contributing to SOD. In our study different RNA preservation methods were tested to preserve microbial RNA in FFT sample. The results confirmed that LifeGuard(TM) Soil Preservation Solution (MO BIO Laboratories, Inc, California) is the best preservative method for RNA preservation. Through T-RFLP analysis of 16s rRNA and 16s rDNA, SRB's (Sulfate Reducing Bacteria) are shown to dominate the FFT during initial stages of incubation but its population decreased significantly over-time. This observation suggests that sulfate reduction is a self-limiting process and has less impact on the quality of overlying water column.