The growth of iron particles by thermal decomposition of Fe(CO)5 in a tubular reactor was analyzed by using a one dimensional discrete-sectional model with the coalescence by sintering of neighboring particles incorporated in. A thermal decomposition of Fe(CO)5 vapor to produce iron particles was carried out at reactor temperatures varying from 300 to 1,000 ℃, and the effect of reactor temperature on particle size was compared with model prediction. The prediction exhibited good agreement with experimental observation that the primary particle size of iron was the largest at an intermediate temperature of 800 ℃. Model prediction was also compared with Giesen et al.’s [1] experimental data on iron particle production from Fe(CO)5. Good agreement was shown in primary particle size, but a considerable deviation was observed in primary particle size distribution. The deviation may be due to an inadequate understanding of the sintering mechanism for the particles within an agglomerate and to the assumption of an ideal plug flow in model reactor in contrast to the non-ideal dispersive flow in actual reactor.