Friction stir welding ( FSW) is a novel welding technique which has been successfully applied in structure manufacturing of aluminum alloys (including 2XXX and 7XXX). It is indicated that friction stirring in aluminum alloy weld can produce very fine grain size. This paper deals with the SPF response in 1420 Al-Li alloy welds. The results shows that the friction stir weld Of 1420 Al-Li Alloy could achieve good superplasticity performance. The lateral elongation in the weld could reach 120% and the grain size still remains almost the same. And the drawback in the friction stir weld is the obstacle to fulfil the good SPF ability. During the friction stir welding, some oxides or contaminates were stirred into the weld in the form of black line. When the weld was experienced superplastic deformation, the crack initiated from the line and finally reach the surface and bottom of the plate. It is suggested that the parameters and preparation before welding must be optimized so that the weld can achieve maximum superplasticity performance.