Synthesis of anisotropic Ag nanoprisms (AgPRs) contributes to the development of high performance plasmonic devices. The localized surface plasmon resonance wavelength of AgPRs was successfully tuned within 500-600 nm by sequential irradiation of 470-nm and 525-nm light to the Ag nanospheres for predetermined periods of time. We have clarified the mechanism in which the AgPRs are synthesized by the first irradiation, which act as the seeds for the growth in the second irradiation with remaining Ag nanospheres being consumed.