The diffusion of boron in yB2O3(1-y)SiO2 glasses with up to 8 mol% B2O3 was investigated by annealing doped layers on the inner surface of quartz glass tubes between 1700°C and 2000°C and measuring radial doping profiles by X-ray microprobe analysis and refractive index profiling subsequent to the tube collapse. By comparison with calculated profiles, diffusion coefficients could be determined and fitted by an Arrhenius function, where the preexponential D0 = 100.38 cm2s−1 is constant, but the activation energy decreases with increasing concentration according to E = (449-4.8·c^1.06) kJ·mol−1 (c[mol% B2O3] = 100y).