We report the study of surface-enhanced Raman scattering (SERS) and photocatalytic reactions of methylene blue (MB) adsorbed on cubic silver oxide (c-Ag2O) nanocrystals. The SERS, activities of MB observed on c-Ag2O are surface coverage dependent. According to the SERS selection rules, the strong intensities of the C-S-C and C-N-C bending modes imply that the MB molecules are adsorbed on the c-Ag2O surface with a near perpendicular position. On the other hand, if these modes are weak, MB assumes a near-parallel position to the c-Ag2O surface. Under the "perpendicular" condition, the photocatalytic reaction rate of MB observed on c-Ag2O surfaces is first order at a high surface coverage, whereas under the "parallel" condition, the observed rate is zero order at a low surface coverage. The SERS intensity trends and the kinetic behavior of MB on c-Ag2O are correlated.