Objective To investigate the effectiveness of free anterolateral thigh flap (ALTF) with fascia lata in repairing diabetic foot ulcers (DFUs) with bone exposure. Methods Between January 2019 and January 2021, 20 patients with DFUs with bone exposure were admitted. There were 17 males and 3 females with a median age of 57.5 years (range, 48-76 years). There were 10 cases of Wagner grade 3 and 10 cases of grade 4. The DFUs formed 1 to 14 months, with a median time of 3 months. The patients underwent CT angiography of both lower extremities, which showed extensive atherosclerosis in both lower extremities; 6 of them were severely narrowed or occluded and underwent percutaneous transluminal angioplasty. The size of wound ranged from 7 cm×6 cm to 27 cm×10 cm after applied first-stage debridement combined with vacuum sealing drainage treatment. In the second-stage, free ALTF with fascia lata was used to repair wounds and partial defects of tendons. The size of flap ranged from 8 cm×5 cm to 28 cm×11 cm. The wound of the donor site was sutured directly. The survival of the flap, the healing time of the wound, and the complications were recorded. The laser speckle blood flow imaging system was used to detect the blood perfusion of the flap and the skin around the flap at 2 weeks and 6 months after operation. The foot function was evaluated by American Orthopaedic Foot and Ankle Society (AOFAS) score at 6 months after operation. Results After operation, effusion under the flap happened in 6 cases, which was cured after symptomatic treatment. Flaps survived completely in 14 cases. The tissue necrosis at the edges of the flaps in 3 cases healed after dressing changes. Venous crisis of flaps occurred in 3 cases, of which 1 case was completely necrotic after exploration, and the other 2 cases were partially alive. The wounds of 3 cases were repaired with skin grafts after debridement and dressing. The flap survival rate was 95.0%, and the limb salvage rate was 100%. The wound healing time after flap transplantation was 14-30 days, with an average of 19.1 days. Two patients had recurrence of peripheral skin ulcers of the flaps within 1 month after healing, which healed after conservative dressing changes. Eighteen cases of incisions at donor site healed by first intention, 2 cases had local skin necrosis and healed by debridement and suture. All patients were followed up 6-30 months, with a median time of 11 months. The texture, appearance, and elasticity of the flaps were good. All patients could walk alone without pain. At 6 months after operation, the AOFAS score was 75.8±11.9, which was significantly different from that (44.7±18.4) before operation (t=−7.025, P=0.000); The blood perfusion value increased from (38.1±7.8) PU at 2 weeks to (42.7±10.3) PU, and the difference was significant (t=−4.680, P=0.001). Conclusion Free ALTF with fascia lata has a rich blood supply and a high survival rate. It can be used to repair DFUs with bone exposure. After the free skin flap healed, it can promote revascularization of the affected foot, reduce the probability of ulcer recurrence, and avoid amputation.