The electric Ohm resistivity of electroless Cu depositions on dielectric substrates as a function of their thicknesses is studied. Substantial deviations (up to 10–20 times) from the standard resistivity (ϱ∞ = 1.7 μΩcm−1) below 0.5 (μm thicknesses are observed. The experimental data show for the entire region of thicknesses (d∞ ∼ 0.07–5 μm) a power function between the relative resistivity changes (Δϱ/ϱ∞) and the inverse thickness of depositions (d∞)−(Δϱ/ϱ∞ ∼ (1/d∞)0.8. This empirical relation is discussed as an effect of the porous structure of the metallic layers deposited on the substrate. A scanning electron micrography was applied in order to visualize the morphology of the depositions. The micrographs clearly show the evolution of the deposition profile: starting from separate islands at the very beginning of the process, and gradually covering the entire area with continuous but porous metal layers.