This paper is the first report on transmission loss of screenprinted metallization of transmission lines at frequencies ranging up to 340 GHz. We observed that the printed transmission lines exhibited significantly reduced transmission losses when compared to conventional lines on the commercialized impedance standard substrate (ISS). The conductivity of Ag metallization was considered the reason for this reduced loss. Though degradation of the loss was observed in transmission lines approximately 3 years post fabrication, the printed line retains a smaller loss than conventional lines on the ISS. Further, despite the printed line having inferior production reproducibility, the screen-printed technology was considered to be an improved solution for the fabrication of millimeter-wave circuits, even in the 300 GHz band.