Abstract: An Al₂O₃ short fibre reinforced Al-12Si matrix composite was prepared using sqeeze cast method.T he process of fracture and crack nucleation of the composite were studied by in-situ observation in transmission electron microscope.The results show that the fihre matrix interface is one of the fracture courses of the composite.Also thefailure of the fihre resulting from crack initiation and propagation in it was observed in the experiment.