Crystallization of 50-nm-thick a-Si was achieved with smooth surface using Blue Multi-Laser Diode Annealing (BLDA). The a-Si films were deposited by RF sputtering or chemical vapor deposition, and annealed by BLDA of CW mode. After annealing in relatively lower laser power, RMS value was slightly increased, but smoothness was kept even if the condition that the films were crystallized. BLDA has a potential to realize a next generation poly-Si TFTs.