Temperature-programmed desorption of a [p(2 × 3)-N + p(2 × 1)-O] Ag(110) surface gives simultaneous desorption of N2 and NO at 520 K and the desorption of O2 at 600 K. The STM image showed a competitive array of (Ag4N) rows and (-Ag-O-) strings. N2 is formed by self-recombination of N-atoms, and NO is formed by the reaction of N-atoms with (-Ag-O-) strings. The spatial distribution of NO (520 K) took two maxima, in the normal and ca. 17° off-normal directions, although N2 and O2 desorb only in the normal direction. These two maxima may reflect the reaction of N-atoms with O-atoms at the terminal and inside of the (-Ag-O-) strings.