A continuous synthesis process for TiO2, particles using a slug flow tubular reactor is A modelled using population balance equations. In this reactor, continuous liquid feed is separated into small portions by injecting nitrogen gas, so that each liquid portion can be treated as a batch reactor. It is assumed that each particle consists of nuclei, and the particles grow by aggregation of particles. A fixed number of nuclei, N-agg, is regarded as a constituent unit of particle growth to reduce the number of governing equations. By using a reduced number of equations, mean particle size, conversion to particles, geometric standard deviation, and particle number density are fitted to the experimental data. The fitted results explain well the fact that a higher initial H2O concentration gives a higher conversion, larger particle number density and smaller mean particle size. Simulated results of particle size distribution using estimated constants of reaction rate and particle interaction energies are also in agreement with the experimental data. Aggregation between small particles and large particles is found to be dominant after large particles are formed.