Amorphous silicon thin films deposited on glass are successfully crystallized by frequency-doubled Nd∶YAG laser with a flat-top beam. Beam shaping optical system of fly′s eye lens array for achieving flat-top beam with uniform intensity distribution is introduced, and with this beam the amorphous silicon thin films is crystallized. The surface morphology of laser-crystallized samples are studied by atomic force microscopy. Raman spectra are measured to confirm the phase transition from amorphous silicon to polycrystalline silicon (poly-Si), and the surface roughness of the thin film after crystallization is enhanced. The grain size and crystallinity are calculated for different laser fluences with Raman spectral data. Both of the grain size and crystallinity evaluated from the data of Raman spectra are found to increase almost linearly with the laser fluence from 400 to 850 mJ/cm2. However, the Raman signal for poly-Si disappeares when the laser fluence exceeds 1000 mJ/cm2. In this experiment, it is about 850 mJ/cm2 to produce the best crystallization.