【Patient selection】This study is approved by The Institutional Review Board on Human Studies. The procedures are performed in accordance with the standards of the Ethical Committee and the Declaration of Helsinki in 1975. All patients are required to sign an informed consent prior to participation in the study. The inclusion criteria include patients with recurrent chronic diabetic ulcers of the extremities for longer than 3 months duration. The exclusion criteria include patients with cardiac arrhythmia or pacemaker, pregnancy, skeletal immaturity patients with malignancy, patients with joint sepsis, ulcers around the skull, spine and chest wall, and patients with poor compliance. A power analysis revealed that a sample size of 32 in each group would be required to establish the statistical significance with α = 0.05 and power = 0.8. We anticipate a drop-out rate of 10 to 15% for various reasons during the course of treatment. Therefore, we plan to recruit 100 patients in the study. Patients are randomly divided into two groups with 50 patients in the shockwave group, and 50 patients in the HBO group who are treated with HBOT. All patients receive the same protocol of diabetic control, wound care, antibiotics and corrective shoe wear etc. Pre-treatment evaluations include complete history and physical examination, chemistry and coagulation profiles, detailed past surgical and medical treatments. The ankle-brachial index (AKI) and HBA1C are assessed individually.