A model has been developed for spray pyrolysis reactor, considering continuity, momentum, energy and mass balances in the reactor. By numerical integration of model equations, the profiles of gas temperature, gas stream velocity and aerosol concentration are shown inside the reactor and the paths and temperature histories of aerosols are described along the reactor. Aerosols are moving toward the center of spary pyrolysis reactor in thr radial direction by thermophoresis and aerosols are not found in the region near the reactor wall. The radial gas stream velocity is significant around r/R=0.5 and is in the direction toward the center of reactor when the gas flow is heated rapidly. As the gas flow rate increases, aerosols begin to have less residence time under pyrolysis temperature iinside the reactor and the diference of tem-perature histories of aerosols increases depending on the initial locations of aerosols at the reactor inlet.