Abstract: Microstructure and mechanical properties of Be/Al weld were analyzed with nano indenter.The results showed that there are beryllium phases embedded in the aluminum matrix in the fusion zone.The microstructure of the fusion zone is low melting point phase that enlarged the region of weld solidification temperature and brought great thermal stress,especially at the side of beryllium.There are the certain gradients of microhardness and elastic modules at the interface of Be/Al welded joint.The microhardness and elastic modules are not stable at beryllium side of joint zone,which indicates that there exist brittle phase at heat affected zone.So the welding cracks nucleated easily at beryllium side of welding zone.