【Background/Purpose】Patients with diabetic peripheral neuropathy (DPN) experience an increased risk of falls and decreased quality of life due to impaired balance and gait. This study aimed to identify factors associated with gait instability in DPN patients. 【Methods】Forty DPN patients (age: 58.8 ± 9.3 years; 16 males, and 24 females) admitted to our hospital for diabetic education were included in the study. The instability in gait was assessed using a triaxial accelerometer, which was affixed to the third lumbar spinous process reflecting the center of gravity. The root mean square (RMS) value was calculated from the data acquired during walking and corrected by the squared value of body weight. Electromyography was used to evaluate the co-contraction of lower leg muscles; the co-contraction index (CI) was calculated for the tibialis anterior and soleus muscles during walking. For each evaluation, data were obtained from a 10 m walk test at the patient’s comfortable speed. Pearson's correlation analysis was used to study the relationship between each parameter. In addition, multiple regression analysis was conducted with RMS as the dependent variable and vibration perception, CI, maximum ankle dorsiflexion muscle strength, and maximum ankle plantarflexion muscle strength as independent variables. Moreover, multiple regression analysis was performed with RMS as the dependent variable, CI as the independent variable, and adjusted for age, gender, and height. 【Results】The results showed that RMS was significantly correlated with the CI of lower leg muscles (β = 0.45, p < 0.01). Further, this relationship remained significant even after adjustment for age, gender, and height (β = 0.54, p < 0.01). 【Discussion】These results suggest that co-contraction of the lower leg muscles affects the overall stability during walking in DPN patients.