The adsorption state of ammonia (NH3) on the ZnO(10 (1) over bar0) surface has been investigated using photoelectron spectroscopy (PES) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The core-level and valence-band PES measurements reveal that ammonia adsorbs molecularly via its N atom on ZnO(10 (1) over bar0) and that no dissociated species are formed at room temperature. The orientation of adsorbed NH3 is investigated by the polarization-dependent N K-edge NEXAFS measurements, and it is found that the C-3v molecular axis of NH3 is inclined in the [000 (1) over bar] direction with the tilt angle of 33degrees-41degrees from the surface normal.