Abstract: Objective of this study was to develop a practical method to prepare nano-size TiO₂ sol for improving environmental risk studies of engineering nano materials. Thus the influences of ultrasound time，different dispersants and quiescent time on the dispersion effect of commercial  nano-size TiO₂ were investigated and a nano-solution with stable dispersion system，small particle size，and high concentration of TiO₂ was prepared.Results indicated that the optimal conditions to prepare the stable nano-size TiO₂ sol was firstly to add 500 mg sodium hexametaphosphate（SHMP） as dispersant in 100 mL ultrapure water， and add 100 mg commercial nano-TiO₂，then lay it aside for 6 d after the 15 min of ultrasound time.Consequently，the average size and TEM characterization size of  nano-size TiO₂ sol were at（196±20） nm and 50~80 nm，and the dispersion mass concentration and Zeta-Potential were（61.89±5.41） mg/L and（-51.3±6.7） mV，respectively.This optimized method could prepare a stable  nano-size TiO₂ sol with high concentration，which would make a good foundation for the study of environment risk of engineering nano-materials.

Key words: nano-size TiO₂；ultrasound time；dispersant, disperse concentration
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