Crystallization of amorphous silicon film was performed successfully by excimer laser annealing(ELA) using KrF laser (wavelength: 248nm). In addition, samples after ELA were investigated by the measurement of UV-Reflectance, AFM and DC conductivity. Grain size was enlarged 250nm on the condition of substrate heating at 400℃ and high energy density below 450mJ/㎠, so that DC conductivity increased several orders of magnitude. But the rough surface was observed at high energy density over 300 mJ/㎠, and conductivity was decreased even though large grain could be obtained. The degree of crystallization was compared by reflectance of wavelength 280nm in UV-Reflectance increasing laser energy density. The optimum condition of laser energy density was around 300 mJ/㎠ for undoped 50nm amorphous silicon film in ELA. The elongated beam was better in unifomity than the rectangular beam. Reflectance of He-Ne laser was not suitable as the control parameter of ELA process because of small difference between the amorphous silicon and polycrystalline silicon of the reflectance at wavelength 632nm.