Pd and Pt nanoparticles (NPs) are fabricated in solution through the photodecomposition of PdCl 2 and H 2 PtCl 6 by femtosecond laser, respectively. The fabrication mechanisms are discussed. The nonlinear optical properties of Pd and Pt NPs are investigated by using Z-scan technique with femtosecond laser at 800nm. With the increase of irradiation intensity, Pd NPs exhibit positive nonlinear absorption (PNA) throughout, whereas Pt NPs experience a transformation from saturable absorption (SA) to PNA. The PNA of Pd NPs is ascertained to the two-photon absorption (TPA) between d band and conduction band. The SA of Pt NPs is attributed to the intraband absorption in conduction band and the mono-photon absorption between d band and conduction band, and the PNA is attributed to TPA between d band and conduction band along with the free carrier absorption. We show that the Pd colloid satisfies the requirements for optical switching.