A p(2x3)-N Ag(110) surface obtained by N+ and/or N-2(+) ion bombardment gave a desorption peak of N-2 at 530 K. When this p(2x3)-N Ag(110) surface was exposed to O-2 at room temperature, the LEED pattern showed a combined structure of [p(2x3)-N + p(2x1)-O]. The STM image proved the growth of the (-Ag-O-) and (Ag2N) strings in the [001] and [1(1) over bar0$] directions, respectively. The TPD spectrum of the combined surface gave the desorption of N-2 at 530 K, NO at 490-520 K, and O-2 at 600 K. When this [p(2x3)-N + p(2x1)-O] Ag(110) surface was illuminated with a UV light at room temperature, the (-Ag-O-) strings in the STM image were selectively erased although the (Ag2N) underwent little influence, and the LEED pattern changed to the p(2x3)-N structure, The TPD spectrum of the surface after the illumination gave only N-2. These results indicate that surface migration of N atoms triggers the reaction between N and N yielding N-2 as well as N and O yielding NO on the surface. Selective photobleaching for the combined structure may suggest a feasibility of atomic scale lithography of the surface by using photochemical reactions.