The formation of Ti and Si nanoparticles by laser ablation of metallic targets in liquid environment is reported. The use of Second Harmonic Generation (SHG) pulsed Nd-YAG laser (532 nm, 15ns, 20 Hz repetition rate) allows a good rate of nanoparticles (NPs) formation. The NPs were characterized by UV-Visible transmission spectrometry and (SEM) scanning electron microscopy. The results show spherical Ti NPs and squared Si NPs. The optical band gap energies of the colloidal solutions were estimated for the two targets as function of the laser fluences.