〔Abstract〕 Objective To investigate the nutritional status of serum 25-hydroxy-vitamin D [25(OH)D] in diabetic patients in Shenzhen. Methods A total of 455 diabetic patients were enrolled in the Endocrinology Department of Shenzhen Second People's Hospital from July 2017 to June 2018, including 231 males and 224 females, aged 18-89 years, with an average age of (59.3 ± 20.6) years. Patients with different genders, different age groups ( < 50 years old, ≥ 50 years old and < 70 years old, ≥ 70 years old), different seasons (summer, autumn, spring and winter). were analyzed the serum 25(OH)D levels. Results (1) The level of 25(OH)D in female patients with diabetes mellitus was higher than that in male patients, and the level of 25(OH)D in male patients was (19.67 ± 5.93) μg·L-1, female patients was (21.27 ± 6.69) μg·L-1, the differences were statistically significant (P < 0.05). (2) The 25(OH)D level of patients increased with age, and the 25(OH)D level of patients < 50 years old was lower than that of patients ≥ 50 years old and < 70 years old, the differences were statistically significant (P < 0.05); (3) The 25(OH)D level was lower in spring and winter than in summer and autumn, and the differences were statistically significant (P < 0.05). Conclusion Deficiency or deficiency of 25(OH)D is common in diabetic patients, especially in male patients, patients < 50 years old, and in spring and winter, attention should be paid to vitamin D supplementation in diabetic patients.