PURPOSE: We aimed to investigate the effects of a high-intensity interval training (HIIT) program on the cardiorespiratory adaption and mitochondria function of patients with T2DM. METHODS: Fourteen patients with T2DM (men/women, 7/7; mean age, 54.6 years; mean hemoglobin A1c, 7.2%) were randomized to either conventional walking training (n = 8) or HIIT training (n = 6; twice weekly for 12 weeks). Cardiopulmonary exercise testing (CPX) was performed at baseline and after training. Moreover, mitochondrial function was assessed using technetium-99m sestamibi (99mTc-MIBI) imaging of both legs after training. RESULTS: After training, 99mTc-MIBI counts of the legs tended to be higher in the HIIT group than in the control group (84.3+19 vs. 65.7+11/pixel; p = 0.08) and was associated with the anaerobic threshold (AT) during CPX (r = 0.64, p < 0.05). The AT increased to a greater extent with HIIT training than with conventional walking training (15.7 vs. -10.0%: interaction: p=0.003). CONCLUSIONS: HIIT training was more beneficial than conventional walking training for increasing AT in patients with T2DM. This result may be linked to the superior effects of HIIT on mitochondrial function within the skeletal muscle