We demonstrate that the surface plasmon resonance of Ag nanoislands (NIs) can be conveniently tuned through the laser power and irradiation time. For instance, the resonance wavelength of Ag NIs can be tuned from 548 nm to 452 nm under the 3 W laser power simply by varying the irradiation time from 5 sec to 2 min. Interestingly, the position-dependent optical absorption spectra and SEM analysis reveals that the Ag NIs gradually disappear from the irradiation center even at 3 W if the irradiation time is longer. This means that the macroscopic diffusion of Ag atoms on the substrate takes place during the CO 2 laser irradiation, and its driving force would be the temperature gradient along the radial direction with respect to the irradiation center due to the spatial beam profile of the laser.