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Electromechanical measurements of plastic deformation phenomena of commercially pure polycrystalline aluminum and copper have been performed at room temperature, where the grain size distribution of test pieces is varied. The room temperature recovery process may reduce their electrical resistivity quite a large percentage, however, some reliable tendencies have been obtained. In aluminum the mechanical hardening curve shows the common tendency and the incremental electrical resistivity varies in two steps with strain up to the instability point in tension. In copper, contrast to the above, both the mechanical hardening and the incremental electrical resistivity curves show common increase with strain. The zero strain electrical resistivity is shown to be inversely proportional to the median of the grain size distribution for aluminum. The incremental electrical resistivity is confirmed to follow the relationship Δρ/ρ_0=C_1ε^K where the exponential coefficient K is shown to be a function of the median both for aluminum and copper.