In this study, a Monte Carlo simulation using an aggregate mean free path model is carried out for the aggregate formation of carbon black in the furnace process at different temperatures. A comparison of the results of two dimensional shape analysis of calculated aggregates and transmission electron microscope images of carbon black obtained from the furnace process shows that the aggregate shapes became complicated with an increase in temperature. In the furnace process, three factors (mean thermal velocity, particle number density, and primary particle diameter) vary simultaneously with temperature. Therefore, investigating the effect of each factor on the aggregate shape requires additional simulations while changing the individual factors. The results of two dimensional aggregate shape analysis shows that an increase in mean thermal velocity and particle number density contributes to complicating the aggregate shape and a decrease in primary particle diameter contributes to its simplification. On the other hand, the mean thermal velocity and particle number density are influenced by both the temperature and primary particle diameter; a decrease in primary particle diameter obviously contributes greatly to an increase in these factors and indirectly contributes to complication of the aggregate shape. Therefore, primary particle diameter is the most important factor in controlling the aggregate shape of carbon black in the furnace process.