Vapor deposited Sm on a Ru(001) surface at 500 K has been investigated by X-ray photoelectron spectroscopy (XPS), temperature programmed desorption spectroscopy (TPD) and work function measurements. The development of a first monolayer can be described as simple adsorption of Sm on the Ru(001) surface. At higher coverages, intermixing of Sm and Ru occurs leading to the formation of a SmRu alloy. The formation of an interfacial alloy above 1 ML coverage is confirmed by Ru 3d core-level photoemission. The average valency of Sm in the alloy phase is determined. Temperature dependent experiments indicate the formation of two alloy phases at the 400-700 and 700-800 K regions. TPD data indicate the zero-order desorption of Sm. Work function changes show that there is a significant amount of charge transfer from Sm atoms to the Ru substrate at low coverages.