Objective To explore the association between serum 25-hydroxyvitamin D [25(OH)D] levels with thyroid nodules (TN) in patients with type 2 diabetes mellitus (T2DM).Methods A total of 335 T2DM patients were enrolled in this study from Xiangyang No.1 People's hospital between October 2021 and October 2022. They were divided into a nodular group (212 cases) and a non-nodular group (123 cases) based on whether they had thyroid nodules. The relationship between TN and 25(OH)D and was explored and factors influencing thyroid nodules in T2DM patients were identified using logistic regression.Results Among 335 patients with type 2 diabetes mellitus (T2DM), the non-nodule group had a higher 25(OH)D level of 18.70 (14.70, 24.20) ng/mL compared with the nodule group with a level of 15.30 (11.15, 20.35) ng/mL. The 25(OH)D level in the single nodule group was 16.30 (12.60, 23.10) ng/mL, higher than the multiple nodule group with a level of 14.50 (10.60, 19.45) ng/mL. The 25(OH)D level in the smaller nodule group was 16.05 (12.35, 21.78) ng/mL, higher than the larger nodule group with a level of 12.15 (10.23, 18.35) ng/mL.Conclusion Vitamin D deficiency may contribute to the occurrence and growth of thyroid nodules in T2DM patients..