The alloying behaviour, including solid solubilities of rare-earths as well as the formation and stability of various intermediate phases in palladium-rich Pd-RE systems were studied by means of the atomic size factor and the reduced transition temperatures. A strong analogy is observed in the plots of the reduced transition temperatures of various intermediate phases against the atomic numbers of rare-earths, and the law proposed by Hume-Rothery and Raynor for dependence of liquidus temperature on atomic radius in simple alloy systems has been extended to more complicated alloy systems.