A series of Ag–Al alloy nanoparticles (NPs) were obtained on the silica substrates by ablating the Ag/Al bilayer thin film with an Nd:YAG fiber pulsed laser at ambient conditions. The corresponding tunability of localized surface plasmon resonance (LSPR) properties and the enhancement of Raman scattering intensity were realized due to the various Ag–Al alloy nanosphere sizes and states of aggregation by varying laser powers. With the increase of laser power, the crystalline quality of Ag–Al alloy NPs was improved with a red shift of the surface plasmon resonance wavelength from 432 nm to 484 nm. Furthermore, the simulation result of finite-difference time-domain (FDTD) showed a substantial agreement with experimental results.