Precise values for the rotational constants of benzene in both the ground and the electronically excited state have been obtained by time-resolved rotational spectroscopy. A relative uncertainty on the order of 10(-5) for these constants has been achieved, while the. absolute values are in excellent agreement with data from rotationally resolved optical spectroscopy. Thus benzene serves as a molecular benchmark for high-resolution rotational coherence spectroscopy (RCS) with the perspective that the influence of vibrations on the equilibrium structure could be studied for a medium-sized molecule by this method soon.