Abstract: The microcracking behaviour of TiAl-based alloys with the duplex and fully-lamellar microstrcutures was studied during compression. It was found that the fracture involves propagation of the existing microcracks and development of more new nuclei, instead of being a nucleationcontrolled event. The lamellar interfaces, especially those having an angle of about 0~30℃ to the loading axis, were found to be the favourable nucleation sites. Microcrack nucleation is likely to be initiated by tensile normal stress concentrated on the lamellar interfaces.