A nanostructured Al-1 %Si alloy containing a dispersion of Si particles in ultrapure aluminum (99.9996 %) was produced by heavy cold rolling to study the effect of second-phase particles on the occurrence of plastic instability during tensile testing of a nanostructured metal. Tensile tests were conducted on the as-deformed sample and on samples after recovery annealing treatments. Work hardening and strain rate sensitivity were studied by tensile test at different strain rates, and deformed and annealed samples were characterized by transmission electron microscopy. By comparing the observed behavior with that of nanostructured commercial purity Al, a significant increase in the tensile elongation was found. This is related to a homogenization of the deformation microstructure due to the presence of finely dispersed Si particles. As a result localized deformation is reduced and tensile ductility increased.