Stresses induced by hydrogen electrosorption in Pdrich Pd-Ru alloys were studied with the use of an Electrochemical Quartz Crystal Microbalance. The total frequency shift was found to be much larger than the frequency shift calculated on the basis of the Sauerbrey equation. The mass frequency shift was subtracted from the total frequency shift to isolate the frequency change due to the formation of the stresses in the alloys lattice. The magnitude of the stresses in the Pd-Ru alloys lattice depends on the amount of absorbed hydrogen (H/M) and the sample composition. The slope of stress-related frequency change vs. H/M plots varies with hydrogen to metal atomic ratio in the whole range of the absorbed hydrogen concentrations studied. The stresses which accompany the absorption process play an important role in the hydrogen absorption/desorption hysteresis effect.