Abstract: Ag@SiO2 core-shell nanoparticles were fabricated via water-in-oil (W/O) reverse microemulsion process. Using sodium borohydride (NaBH4) as reducing agent，the silver core was formed in water droplets and packed with amorphous silicon dioxide (SiO2 shell) formed by the hydrolysis of tetraethyl orthosilicate (TEOS) at the water/oil interface. The obtained nanoparticles were characterized by TEM，UV-Vis and XRD measurements respectively. The diameter of the obtained nanoparticles is approximately from 50 to 100 nm. The size of inner silver core varies by altering the R value (the molar ratio of water to surfactant). The formation of core-shell nanoparticles is affected by the order of ammonia addition. UV-Vis spectra indicated that the plasma resonance absorption of silver core wrapped with SiO2 has a red shift. XRD pattern proved that the nanoparticles have a structure with a crystalline silver core and an amorphous SiO2 shell.