Numerical simulation of polycrystalline silicon particle production by fluidized bed CVD using monosilane is carried out. The model consists of a Kunii-Levenspiel fluidized bed model and reaction kinetics of monosilane pyrolysis in the free space and on particles. Conversion of monosilane, conversion to fines (fines elutriation), and vertical temperature profile in the bubble are calculated using the present model. Effects of scavenging of the fines, deposition on the fines and the temperature profile on the conversions are discussed. The numerical results are compared with the experimental results of Hsu et al,. The numerical results of the conversions in the case of deposition on the fines are larger than those without deposition, while other factors give lower conversions. Consideration of deposition on the fines is found to be essential to explain the experimental results. The diameter of secondary particles of fines agglomerates should be taken into account as a function of bed temperature, It is suggested that the experimentally observed effect of the bed temperature on the fines elutriation is possibly explained when the degree of scavenging or the diameter of secondary particles is increased with increasing bed temperature, both of which are caused by the increase in fines＇ adhesivity with temperature.