In this report, we have studied the effect of temperature-rising-rate on the sizes of nanoscale siliconparticles formed in thermally annealed hydrogenated amorphous silicon (a-Si:H) films. The a-Si:H films wereprepared with electron-beam evaporation in a high-vacuum chamber, then the films were thermally annealedin a furnace at the equilibrium temperature of 620℃ for about 10 seconds but with a high (～100 ℃/min) anda low (～1 ℃/min) temperature-rising-rate in the first stage of their thermal annealing processes, respectively.Using the micro-Raman scattering and the X-ray diffraction techniques, we have found that sizes of the formedsilicon particles change with the temperature-rising-rate in the process of thermal annealing the a-Si:H films.When the a-Si:H films have been annealed with high temperature-rising-rate (～100 ℃/s), the sizes of nanoscalesilicon particles are small in the range of 1.6～15 nm. In the meanwhile, if the a-Si:H films are annealed witha low temperature-rising-rate (～1℃/second), the sizes of nanoscale silicon particles are large in the range of23～46 nm. Using the method of diffusion limited aggregation, we have simulated the growth of nanoscale siliconparticles in a-Si:H films and discussed the effect of temperature-rising-rate on the sizes of the formed siliconparticles.