Submicrometer-grained （SMG） Al-3%Mn （mass fraction） alloy specimens with initial grain size of -0.3 μm were produced by ball milling for 3 h. The Al-3%Mn specimens which were cold rolled with a strain rate of 1×10^-3- 1×10^-2 s-1 at room temperature show high extensibility to failure more than 2500%. Microstructures of pure Al and Al-3%Mn alloy at as-milled and cold-rolled state were examined using X-ray diffraction and transmission electron microscopy （TEM）. Based on the microstructure analysis, it is established that the mechanism of the continued plastic deformation in SMG Al-3%Mn alloy consists of dislocation slip, grain boundary sliding companied by dynamic recovery and recrystallization, and dynamic recrystallization is a main control factor of the large plastic deformation.
