The dynamic deformation behavior on the specimens' surface during the plastic deformation in a solution treated and a T6 treated AA6061 have been measured using an electronic speckle pattern interferometry (ESPI). As a result, the deformation propagations on the specimen surfaces during the tensile deformation were found to be uniform in the early stage of work hardening state in the solution treated alloy. Nevertheless under the work hardening state, the mild strain concentrated necking phenomena were observed at over 18% of plastic deformation. And, this mild strain concentrated necking moved cyclically through the gage region of the specimens. Moreover, the dynamic range of the necking on the specimens decreased as the necking cycle increased. Furthermore, the strain caused by each cycle of the necking movement increased with increasing the cycle of the necking, which then the necking position was finally fixed to the center of the specimens.