Most RNA positive controls currently used for monitoring the quality of RT-PCR assays have some disadvantages, such as instability, inability to monitor the quality of the relevant primers and/or causing indifferentiable false positives. To avoid these disadvantages, a simple method to prepare stable and differentiable RNA positive controls is now demonstrated with a real-time RT-PCR assay for the detection of Nipah virus (NiV). A DNA sequence which was shorter than its counterpart in the NiV genome and contained the binding sites of the primers of the RT-PCR assay was designed, synthesized and inserted into a vector, and then amplified by PCR with two vector-specific primers both of which contained a T7 promoter at the 5' terminal. The RNA positive control was the dsRNA in vitro transcribed from the PCR amplicons flanked by two T7 promoters. The RNA positive control was stable and able to monitor the quality of the whole concerned RT-PCR assay. False positives caused by contaminations of the RNA positive control or its amplicons could be easily identified because the amplicons of the RNA positive control were obviously shorter than those of real positive samples. Thus, the RNA positive control reported in this study avoided some common disadvantages of current RNA positive controls.