Pure rotational transitions of the SF radical in the ground electronic state, (2)Pi, have been measured in the millimeter- and submillimeter-wave region using a spectrometer equipped with backward wave oscillators as radiation sources. The radical was generated by a dc discharge in a gas mixture of SF(6) and He. Forty-four lines have been measured in the frequency range from 248 to 845 GHz, for J values up to 25.5. The accuracy in line position measurement is typically 20-100 kHz, depending on the Doppler broadening. The present data were analyzed by a least-squares-fit procedure using an effective Hamiltonian for (2)Pi states, together with the transition frequencies in the microwave region available in the literature. The molecular constants have been revised with improved accuracy. Copyright 2001 Academic Press.