The self-oscillatory mode of methane oxidation over Pd foil at temperature of 400°C for 1 h caused the formation of a surface layer containing bulky porous agglomerates of nanocrystals. According to SEM data, the agglomerates with diameters of 1–20 μm consisted of crystals ~100 nm in size with pores of similar sizes between them. The agglomerates projected over the surface by 5–10 μm. The catalytic activity of the treated samples in a CO oxidation reaction was measured. The temperature of the onset of the catalytic reaction (CO conversion, 3%) decreased from 400°C for the initial Pd foil to 200°C for the Pd foil after the self-oscillatory oxidation of methane. Results of X-ray diffraction analysis and energy-dispersive X-ray spectroscopy (EDS) allowed us to conclude that the agglomerates observed consisted of the crystals of palladium oxide (PdO). On the contrary, the oxidation of Pd foil surface in a stationary mode was found to promote the formation of a smooth layer of palladium oxide without noticeable porous structures, and the catalytic activity of this layer was lower than that of the Pd sample after self-oscillations. The stability of the obtained porous layers in an inert (He), reducing (H 2 ), or oxidative (air) atmosphere on heating to 700°C was studied. Under the inert or reducing conditions, both the disappearance of palladium oxide and the destruction of nanoparticle agglomerates took place to cause a decrease in the catalytic activity of Pd foil in the CO oxidation reaction. On the contrary, the oxidative treatment caused both an increase in the PdO content of the sample and a growth of the number of porous nanocrystal agglomerates on the surface to result in an additional increase in the catalytic activity of Pd foil.