Monodispersed nanosize titania partciels with a coefficient of variation of 20% (the geometric standard deviation of 1.2) or less were prepared by the hydrolysis and condensation of tetraethylorthotitanate (TEOT) in the presence of hydroxypropylcellulose (HPC). The effects of the TEOT, water, and HPC concentrations on the mean particle size and the coefficient of variation were examined. In the case where the initial TEOT concentration was low and the initial water and HPC concentrations were high, particles of small size were obtained. The particles with low coefficient of variation were obtained at low initial water concentrations, high initial TEOT concentrations and high HPC concentrations. The condition for TEOT of 0.025 mol/dm(3), H2O of 2.0 mol/dm(3), and HPC of 2.5 g/cm(3) in a batchwise experiment gave particles with a mean size of 38 nm and a coefficient of variation of 19% (a geometric standard deviation of 1.20). The monodispersed nanosize fine particles were continuously synthesized using a slug flow tubular reactor. The particles obtained by a continuous experiment were almost the same as those in the batchwise experiment.