Viscosities of B2O3 and TiO2-bearing fluoride-free mold fluxes have been measured by the rotating cylinder method in this work. Effects of different B2O3, TiO2 content, and basicities on the viscosity characteristics have been examined. Viscosity of fluoride-free mold fluxes containing B2O3 and TiO2 was found to decrease with the increase of B2O3, TiO2 content, and basicity. The values of apparent activation energy for viscous flow of slags decrease with additions of B2O3 and TiO2 and the increase of basicity. Two parameters A and B in Riboud model were re-evaluated based on the present experimental data, and the modified Riboud model was used to estimate the viscosity of fluoride-free slag system investigated in present work. The viscosity values obtained by the experimental measurement were in good agreement with those calculated by the modified Riboud model.