In the process of synthesizing Si-nanocrystals (Si-nc) from bulk SiO, the relationship between Si-nc size distribution and annealing condition (temperature from 800 to 1150 degrees C and time from 1 to 16 h) is experimentally investigated by X-ray diffraction and high resolution transmission electron microscopy. It is found that the average size of Si-ncs can be tuned through annealing condition from less than 3 nm to similar to 10 nm, while the size distribution follows a lognormal function with an almost unchanged standard deviation of 0.2. After annealing at even higher temperature (1150 degrees C), two groups of Si-ncs with very different average sizes exist simultaneously and a double lognormal function should be applied to describe the size distribution. (C) 2011 Elsevier B.V. All rights reserved.