Size- and morphology-controlled catalytic colloidal nanoparticles are emerging as novel catalysts for heterogeneous catalysis, but capping ligands adsorbed on the nanoparticle surfaces inherited from the colloidal synthesis always stand as a problem. This perspective highlights recent progress on the influences and removal of capping ligands on catalytic colloidal nanoparticles. Depending on the system, capping ligands can act as either a poison or a promoter for the capped nanoparticles and the underlying mechanisms will be discussed. Various methods for the removal of capping ligands on catalytic colloidal nanoparticles are summarized with an emphasis on a novel controlled oxidation treatment that we recently developed.