We present observational evidence of gravity wave ducting and show, for the first time, that the ducting occurs over large horizontal distances in the mesopause region. An optical network of four all-sky imagers in Japan identified two-dimensional patterns of small-scale gravity wave bands in OH airglow images on 13 June 2004. The wave signatures clearly showed northward propagation of more than 1800 km over a wide range of latitudes. The horizontal wavelength, horizontal phase speed, and wave period were estimated from the airglow data as 33.4 km, 42.8 m s−1, and 13.4 min, respectively. The wave structure lasted for the whole 5-h airglow observation period. Simultaneous MF radar wind data and TIMED/SABER measurements suggested that the wave was trapped and ducted at the airglow height. The ducting likely contributed to the remarkable coherence of the wave as it propagated northward.