The pure rotational spectrum of 175 Lu 16 O in its ground electronic state (X 2 Σ + ) has been observed with a cavity pulsed jet Fourier transform microwave spectrometer. The samples were prepared by laser ablation of Lu metal in the presence of gaseous oxygen, and stabilized in pulsed jets of Ar. The N=1–0 transition has been measured in the v=0, 1 and 2 states. All the observed lines show Zeeman splittings caused chiefly by the Earth’s magnetic field. The transitions show effects of electron spin-rotation structure and of 175 Lu hyperfine structure. Several hyperfine parameters have been evaluated, and are interpreted in terms of the molecular electronic structure. An improved equilibrium internuclear distance, r e , is presented. The results should facilitate astrophysical searches for the molecule.