The influence of magnesium and aluminum salts as impurities on the hydrolysis of titanyl sulfate was investigated. The degree of TiOSO4 conversion to hydrated titanium dioxide (HTD) and the particle size of HTD were measured as functions of the concentrations of MgSO4 and Al-2(SO4)(3) in the TiOSO4 solution. The Boltzmann growth model, which focuses on two main parameters, namely the concentrations of Mg2+ and Al3+ (rho(Mg2+) and rho(Al3+), respectively), fits the data from the hydrolysis process well with R-2>0.988. The samples were characterized by ICP, SEM, XRD, and laser particle size analyzer. It is found that the addition of MgSO4 simultaneously improves the hydrolysis ratio and the hydrolysis rate, especially when F (the mass ratio of H2SO4 to TiO2) is high, hydrolysis ratio increases from 42.8% to 83.0%, whereas the addition of Al-2(SO4)(3) has negligible effect on the chemical kinetics of HTD precipitation during the hydrolysis process, hydrolysis ratio increases from 42.8% to 51.9%. An investigation on the particle size of HTD reveals that the addition of MgSO4 and Al-2(SO4)(3) clearly increases the size of the crystallites and decreases the size of the aggregates.