Microcracks and their effect on the plastic deformation of gamma-TiAl alloy with fully lamellar microstructure (FL) at relatively low strain rate (1 x 10(-5)/s) has been investigated. It is found that a large number of microcracks nucleate within the grains. The microcrack density increases with the increase of grain size. Most of the microcracks nucleate at the gamma/alpha(2) interfaces and gather at grains with soft-orientations. Based on the observation and analysis, a model of microcrack nucleation in FL gamma-TiAl alloy is built up. The plastic elongation of gamma-based TiAl alloys with FL microstructure changes non-monotonously with the increase of grain size, which results from cooperation of micro-deformations and microcracks. (C) 2004 Kluwer Academic Publishers.