The kinetics of the clean-off reaction of O adatoms by CO on Ag(110)-([Formula presented])-O is investigated by scanning tunneling microscopy. The reaction is accelerated in the lower O coverage range where AgO chains with ([Formula presented]) ([Formula presented]) configurations show significant structural fluctuation. Simulations based on the Ising model are used to provide a quantitative understanding of the acceleration, which originates from the dynamical formation of active O adatoms by fluctuation of AgO chains. © 2003 The American Physical Society.