Ferromagnetic behaviour has been experimentally observed in palladium nanoparticles, NPs, prepared by different chemical methods. On the one hand, stabilised palladium NPs using a surfactant and on the other hand alkanethiolate-capped palladium NPs. High resolution transmission electron microscopy, HRTEM, has been used for characterize both set of samples. The average mean size is 2.4 nm for particles dispersed with surfactant and 1.2 for the thiol protected Pd NPs. Magnetic measurements have been performed using a quantum design SQUID magnetometer. Ferromagnetic behavior is evidenced by the hysteresis loops observed even at room temperature for stabilised palladium NPs using a surfactant and for both thiol protected NPs. In this report, different effects are discussed as possible contributions for the onset of ferromagnetism: the presence of twin boundaries and surface effects for the particles dispersed with a surfactant as well as the strong covalent interaction involving some charge transfer (including d charge) from the nanoparticle to the thiol and the effect of the spin-orbit coupling for the thiol protected ones. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)