The strain rate sensitivity of A6061 aluminum is examined as a function of aging condition. The triaxial stress is changed by notched specimen. Increasing triaxiality under high strain rate condition increases flow stress and size of void. No difference of the mechanical properties is found for the results between peakaged and overaged specimens under different strain rates. Plastic constraint factor under high strain rate with notched specimen decreases. The voids initiation, growth and coalescence under high strain rate are promoted by notch, then, the formation of cup-cone type failure takes place. This is accompanied by a concomitant increase in reduction of area with increasing strain rate. The effects of triaxial stress and strain rate on the fracture surfaces are also discussed.