Aims: To assess the limit of detection (LOD) and the feasibility of 16S rRNA-based reverse transcription-PCR (RT-PCR) assays for advanced detection of mycoplasma contamination in cell substrates. Materials and Methods: The RT-PCR approach is based on detecting the 16S rRNA molecules that, in contrast to genomic bacterial DNA, are represented by multiple copies in mycoplasma cell. The number of 16S rRNA molecules in mycoplasma cells of five species i.e. Mycoplasma arginini, Myc. fermentans, Myc. hyorhinis, Myc. orale and Acholeplasma laidlawii, all known to be frequent cell line contaminants in industrial and research laboratories, was measured using molecular methods. The results of two independently prepared mycoplasma cultures harvested at the stationary phase of their growth showed that the 16S rRNA copy number per cell varied in the range from about 400 to 2000 copies, depending on species, but stayed close between different preparations of one species. The assessment of the LOD of the in-house 16S rRNA-based RT-PCR was performed using samples of MDCK cell culture spiked with different amounts of five aforementioned mycoplasma species. To minimize the bias in methods comparison, the LOD of the RT-PCR assay was expressed in terms of genome equivalents (GEs) and compared with that determined for highly optimized 16S rDNA-based mycoplasma testing methods previously described in scientific literature. Conclusions: The results of the study showed that the in-house 16S rRNA-based RT-PCR assay was able to reliably detect the presence of less than one mycoplasma GE that is at least 10-fold higher of the LOD previously determined for well-optimized 16S rDNA-based assays developed and described by other researchers. Significance and Impact of the Study: The results of the study showed that rapid RT-PCR methods based on the detection of bacterial 16S rRNA are able to expedite mycoplasma testing of cell cultures (1-2 days vs 28 days) and to ensure the limits of detection comparable to that of currently used culture-based mycoplasma testing methods.