Noble metallic nanosurface exhibits both plasmonic and catalytic functions. Surface-enhanced Raman scattering of para-aminothiophenol (p-ATP) was measured on a highly uniform two-dimensional silver nanoparticle array at different intensities of an excitation laser (532 nm) ranging from 4 to 4000 W/mm(2). It was observed that p-ATP was chemically transformed to 4,4'-dimercaptoazobenzene (DMAB) with the laser intensities of >= 40 W/mm(2) during the Raman measurement. At 4 W/mm(2), the Raman peaks of DMAB disappeared, which indicates that the laser intensity was insufficient for the chemical transformation although it was sufficient for the Raman measurement. The highly uniform silver nanoparticle array allowed quantitative analysis on the Raman peak intensity. The threshold of the chemical transformation from p-ATP to DMAB was estimated to be similar to 48.8 W/mm(2) on the silver nanoparticle array whose enhancement factor is similar to 10(4).