Polycrystalline Si (poly-Si) thin films for application to display devices and solar cell are generally fabricated by crystallizing amorphous Si (a-Si) thin film precursors. In this paper, studies on Ni-induced lateral crystallization of a-Si thin films by microwave annealing at low temperature were reported. The crystallization of a-Si thin films was enhanced by applying microwaves to the films. The poly-Si films were invested by Optical Microscopy, X-ray Diffraction (XRD) , Raman Spectroscopy and Scanning Electron Microscope(SEM). After processing of Ni-induced lateral crystallization by microwave annealing above 500°C, the a-Si has begun to be crystallized with large grains having the main (111) orientation. The rate of crystallization at 550°C is about 0.033μm/min. Compared to Ni-induced lateral crystallization by conventional furnace annealing, Ni-induced lateral crystallization by microwave annealing both lowers the crystallization temperature and reduces the time of crystallization. The crystallization mechanism during microwave annealing was also studied. The technique that combines Ni-induced lateral crystallization with microwave annealing has potential applications in thin-film transistors (TFT’s) and solar cell.