Fibula flap is widely used in reconstruction work, whereas the low extremity blood supply alteration was unclear. This study would observe the blood oxygen saturation change of foot after harvesting fibula flap. The regional tissue oxygen saturation (rSO2) of the lateral side and inner side of feet was measured using near-infrared spectroscopy oxygen monitoring system (NIRS) before operation and in postoperative day 1 to 7, and the foot of the control side was measured as control. The rSO2 of the donor side foot decreased less than 5% (P < 0.05) in the first 8 hours after operation and recovered to the level of the control side later. NIRS is ideal for measuring rSO2 of donor side foot after fibula flap. The rSO2 of the donor side foot decreased less than 5% after fibula flap harvesting.