Background: Diabetic lower extremity ulcer, including diabetic foot ulcer (DFU) and leg ulcer, is one of the refractory complications of diabetes, the treatment of which is challenging, expensive, and lengthy. Recombinant Human Granulocyte/Macrophage Colonystimulating Factor (rhGM-CSF) is an immunomodulatory cytokine that has been mainly applied in the treatment of hematological diseases. Clinical evidence regarding GM-CSF in the treatment of diabetic lower extremity ulcers is limited. This study is the first case series that investigates the repurpose effects of rhGM-CSF on diabetic ulcer healing in real clinical practice. Methods: Nine patients diagnosed with diabetes and refractory lower extremity ulcer (ulcer duration >2 weeks) were included from September 2021 to February 2023 in the Division of Endocrinology, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology. Patients with Wagner grade >4 and SINDAD >5 were excluded. The included subjects were treated with rhGM-CSF plus standard of care (SOC) including glycemic control, foot care education, debridement of necrotic tissues, topical wound dressings, offloading, and infection control when necessary. The observation endpoint was complete epithelialization. Their clinical manifestations, laboratory tests, and therapeutic effects were extracted and analyzed. Results: The case series included 9 cases aged from 29 to 80 years and all the patients were male. Seven of 9 patients presented neuropathic ulcer. Only one case showed non -infected ulcer from tissue samples and one case presented ankle brachial index (ABI) <0.9. It was observed that the ulcer areas among these 9 patients gradually declined throughout the whole treatment period with the average healing velocity 0.32 +/- 013 cm(2)/day and the mean time to complete healing 16.0 +/- 3.7 days. The relative area (percentage of initial ulcer area) decreased to 66.7 +/- 13.0% on average after the first treatment. Ulcers in all the 9 patients achieved complete epithelialization after 4-8 times treatments. Conclusion: The case series suggests rhGM-CSF as a promising therapeutic strategy for the treatment of diabetic ulceration. More robust data from randomized controlled trials are required to further evaluate its clinical efficacy.