The effects of selective Si + ion implantation on excimer laser annealing (ELA) of PECVD a-Si thin film were investigated. The selective Si + ion implantation was employed to amorphize a-Si film locally and the lateral grain growth was successfully induced. In the selectively implanted region, the threshold excimer laser energy for a-Si melting was 85mJ/cm 2 while that of the implanted region was 105mJ/cm 2 , which may be attributed to the fact that high-energy implantation with high density may amorphize a-Si film effectively and may weaken atomic bonding energy in the implanted a-Si film. Periodically arranged lateral grains were successfully formed near the implanted region and grain size was up to 1μm.