Effect of the mechanical activation of Gd2O3, Dy2O3, Ho2O3, and Lu2O3 oxides on surface tension σ and density ρ of borate melts is studied. Linear temperature dependences of σ and ρ are found, and the temperature coefficients are calculated. The dependence of σ on the lanthanide number in the periodic table is found and exhibits nonmonotonic behavior of the melts. The effect of mechanical activation on σ and ρ is explained by the formation of complex lanthanide ions, which have uniform geometry in the borate melts.