The effect of preparation parameters on the particle size of silicon nanocrystallite produced by laser-induced chemical vapour deposition (LICVD) was studied. It is found that the particle size of nano-Si prepared by LICVD is related to preparation parameters. We obtained the optimum synthesis parameters for preparation of the right sized nano-Si powder produced by LICVD. The effect of different annealing treatments on the infrared (IR) absorption bands of the nanosized silicon was also investigated.