The millimeter-wave rotational spectrum of ethanetellurol has been recorded and assigned for the first time. The spectroscopic study has been complemented by high level ab initio calculations. Geometries, total electronic energies, and harmonic vibrational frequencies have been determined at the MP2 level. A small-core relativistic pseudopotential basis set (cc-pVTZ-PP) was employed to describe the tellurium atom. Two stable conformers, synclinal and antiperiplanar, have been identified. Both theory and experiment have shown the synclinal form to be more stable by 2 kJ/mol. The doublet structure observed in the rotational spectrum of synclinal conformer is attributed to tunneling motion of tellurol functional group. The energy difference between 0(+) and 0(-) substates split by tunneling has been determined from the observed spectra.