In this study, the effect of thermal oxidation on fatigue behavior of Ti6Al4V and Ti6Al7Nb alloys has been examined. Thermal oxidation was carried out by holding the alloys at 600 degrees C for 60 h in normal atmospheric condition. Upon thermal oxidation the surfaces of the alloys were covered with a 1-2 mu m thick oxide layer supported by a 6-7 mu m thick oxygen diffusion zone. Thermal oxidation caused considerable increase in surface hardness without altering the tensile properties (with the exception of yield strength) significantly. When compared to the as-received state, thermal oxidation caused a reduction in rotating bending endurance limit almost about 30% for Ti6Al4V alloy and about 10% for Ti6Al7Nb alloy.