The effects of oxidation on strain relaxation in Si1-xGex layers on silicon substrates were investigated. Si1-xGex layers, with different Ge fractions (x=0.15 and 0.3), were grown on chemically cleaned silicon substrates by an ultrahigh vacuum chemical vapor deposition process. Oxidation at 800 and 900 °C under O2 ambient in a tube furnace resulted in the production of silicon oxide layers on top and a Ge-rich region in the Si1-xGex films. It was observed that the oxidation of Si0.85Ge0.15 films at 900 °C produced the relaxation of the misfit strain in the remnant Si1-xGex layer and the increase in strain in the Ge pile-up layer with increasing oxidation time, while the oxidation at 800 °C produced no changes in the misfit strain in the Si1-xGex layers. The oxidation of Si0.70Ge0.30 films at 800 °C showed the relaxation of the misfit strain in the remnant Si1-xGex layer with the accumulation of stain in the Ge pile-up layer. However, the oxidation of Si0.70Ge0.30 layers at 900 °C exhibited the strain relaxation in the Ge pile-up layer after - - the Ge pile-up was extended into the remaining Si1-xGex layer, with the formation of misfit dislocations at the interface between the remaining Si1-xGex and Si substrate.