The in vitro transcription termination efficiencies of a phage T7 terminator T$\varphi$ for the T7 and SP6 RNA polymerases were studied. Amounts of transcription terminated by T$\varphi$ were compared with amounts of read-through transcripts run off at a restriction site. For quantitative analysis the transcripts were labeled with [a-32P] rNTP in invitro transcription reaction. Transcription of T7 RNA polymerase terminates with efficiency of 38\% by the T$\varphi$ in the pGEM3Z, but with increased efficiency in the pET-3. Interestingly, the T$\varphi$ shows 81\% termination efficiency for the SP6 RNA ploymerase. Now this becomes the first strong terminator discovered for the SP6 RNA polymerase. This also suggests that both RNA polymerases might share a similar mechanism of transcription termination.