Thiol-functionalized ionic liquid (TFIL: 1,3-di(2',3'-dimercaptoacetoxypropyl) imidazolium, 3''-mercapto-1''-propanesulfonic acid) as a stabilizer for preparing palladium (Pd) nanoparticles was synthesized. The suggested TFIL was designed to have thiol groups on both cation and anion as well as on symmetrical positions in cation. Transmission electron microscopy (TEM) shows that the average diameter of the palladium nanoparticles was 3.0 nm and that the standard deviation was 0.15 nm. The overall results strongly suggest that this potential TFIL can act as a highly effective stabilizer for the preparation of Pd nanoparticles.