Using a simple model for the structure of oxygen in silicon and germanium crystals and making the assumption that internal friction and diffusion are both due to the same relaxation phenomenon, the diffusion coefficient of oxygen was calculated from experimental data on internal friction. The results are: D = D 0 exp − ( U kT ) ; O in Si: D 0 = 0.21 cm 2/sec, U = 2.55 eV; O in Ge: D 0 = 0.17 cm 2/sec, U = 2.02 eV. The calculated values of D are in reasonable agreement with available experimental data.