A novel resistometric technique enables the investigation of single void nucleation and growth induced by electromigration (EM) for aluminum (Al) lines having a perfect bamboo structure in comparison with single‐crystal Al lines. Fine tungsten (W) voltage probes were fabricated at every 4 &mgr;m along the Al line with grain sizes of 10 &mgr;m or more. Local electrical resistance changes have confirmed that a void nucleated only at the grain boundary and no damage appeared within the grains. The measured values of the local electrical resistance changes were converted to EM‐induced void growth rates. The vacancy flux was deduced from the void growth rate under the assumption that a vacancy volume is equal to the atomic volume. It has been clarified that the vacancy fluxes for a bamboo‐structured Al line were about one order magnitude smaller than the ideal vacancy fluxes in the Al lattice derived from the Nernst–Einstein relation. The vacancy fluxes for single‐crystal Al lines were also quantified under an accelerated test at a high electric current density with a temperature gradient. These results suggest that the bamboo grain boundaries have a blocking effect on vacancy flow. This blocking produces vacancy supersaturation near the grain boundary, and the reduction in vacancy flux is well explained by the back‐diffusion due to the corresponding concentration gradient.