To investigate the relationship between serum vitamin D levels, platelet-to-lymphocyte ratio (PLR), and peripheral neuropathy in patients with type 2 diabetes mellitus (DPN). Methods: A total of 256 patients with type 2 diabetes mellitus who were hospitalized from August 2021 to January 2023 at the Endocrinology Department of Xiaogan Hospital affiliated with Wuhan University of Science and Technology were selected as research subjects. Based on whether they had DPN, they were divided into two groups: 124 cases with simple type 2 diabetes mellitus were included in the control group, and 132 cases with type 2 diabetes mellitus complicated by DPN were included in the observation group. The patients’blood pressure, height, and body mass index were measured; routine blood tests, blood glucose, lipid profiles, glycosylated hemoglobin (HbA1c), serum 25-hydroxyvitamin D [25(OH)D], and other biochemical indicators were tested, and the PLR was calculated; the differences between the two groups in PLR, 25(OH)D, and other indicators were compared. Logistic regression analysis was used to identify independent risk factors for the development of DPN, and Pearson correlation analysis was used to determine the correlation between PLR and serum 25(OH)D, as well as other biochemical indicators. Results: The observation group had higher ages, duration of diabetes, systolic blood pressure, platelet count, fasting blood glucose, HbA1c, low-density lipoprotein cholesterol (HDL-C), triglycerides (TG), and PLR than the control group; high-density lipoprotein cholesterol (HDL-C), lymphocyte count, and serum 25(OH)D were lower than the control group; all differences were statistically significant (P<0.05). Logistic regression analysis showed that PLR, age, duration of diabetes, HbA1c, and LDL-C were risk factors for the development of DPN in patients with type 2 diabetes mellitus, while vitamin D was a protective factor against DPN (P<0.05); when serum 25(OH)D < 31.72 ng/mL, it could effectively indicate the risk of developing DPN (P<0.05); Pearson correlation analysis found that PLR was positively correlated with age, duration of diabetes, body mass index, systolic blood pressure, fasting blood glucose, HbA1c, LDL-C, and TG (P<0.05); but negative- ly correlated with HDL-C and serum 25(OH)D (P<0.05). Conclusion: PLR is one of the risk factors for the development of DPN, while vitamin D is a protective factor against DPN. Moreover, PLR is negatively correlated with vitamin D levels.