A method of fabrication a polysilicon layer is provided. A substrate is provided and then a buffer layer having a plurality of trenches thereon is formed over the substrate. Thereafter, an amorphous silicon layer is formed over the buffer layer. Finally, a laser annealing process is conducted so that the amorphous silicon layer melts and crystallizes into a polysilicon layer starting from the upper reach of the trenches. This invention can be applied to fabricate the polysilicon layer of a low temperature polysilicon thin film transistor liquid crystal display such that the crystals inside the polysilicon layer are uniformly distributed and have a larger average size.