The pure rotational spectrum of LiS (X(2)Pi (i)) has been recorded in the v = 0 and v = 1 states in the region 130-540 GHz using millimeter/sub-millimeter direct absorption methods. This radical was synthesized from lithium vapor and CS2 in a DC discharge. Transitions arising from the two orbit components were measured, both which exhibited lambda-doubling and, for the Omega = 1/2 ladder, hyperfine interactions. Rotational, lambda-doubling, and hyperfine parameters have subsequently been determined. These data prove unambiguously that the ground state of Lis is (2)Pi (i) and suggest that the A(2) Sigma (+) state lies similar to 4300 cm(-1) higher in energy. The bonding in this radical appears to be predominantly ionic,