It was found that terminator-distal sequences affect transcription termination efficiency of phage T7 terminator Tφ in vitro. The transcription termination efficiencies of plasmids containing terminator-distal sequences, especially near-promoter sequences forming stem-and-loop structure RNA were much higher than those of plasmids without the sequences. Also, the same phenomenon was found for SP6 RNA polymerase with its own promoter and Tφ as terminator. However, these two systems showed different responses to the variation of rGTP concentration. The termination efficiency of T7 RNA polymerase was constant when the concentration of rGTP was increased, be that of SP6 RNA polymerase was decreased as the concentration of rGTP was increased. Our results suggest that the mechanism of factor-independent transcription termination should be more complex than it has been known.