An investigation was conducted to determine the causes of weld defects in laser Be/Al weldments. In agreement with earlier studies, features on the fracture surfaces consistent with hot shortness cracking were observed. In this paper, conduction mode welds and keyhole mode welds were used to produce specimens. Closer examination of the fusion zone crack regions reveals the cracking is a result of thermal stress, shape of welds root and impurities segregation. The defects type relate to the weld parameters, the cracks nucleate easily at conduction mode weld, and the blowholes appear easily in keyhole mode weld.