Background: Type 2 diabetes mellitus is a chronic metabolic condition caused by either a reduction in insulin secretion and/or effect. It affects more than 90% of all diabetic patients. Diabetes is a complex illness that is brought on by a number of genetic and environmental (diet and lifestyle) risk factors working together. On average, one person dies from diabetes-related complications every eight seconds throughout the world. Also, according to a recent International Diabetic Federation (IDF) survey, 537 million persons aged 20-79 years are now living with diabetes worldwide. It is expected to increase to 783 million (12.2%) by 2045. Furthermore, 240 million individuals globally have undiagnosed diabetes. Therefore, there is a rising interest in studying the possible therapeutic value of fat-soluble micronutrients like vitamin D for preventing or controlling type 2 diabetes mellitus. Aim of Study: The present study was designed to evaluate levels of vitamin D in patients with type 2 diabetes mellitus. Patients and Methods: To achieve this aim, in a case-control study conducted in Diyala governorate at Baqubah Teaching Hospital and Balad Ruz General Hospital from first of January to the end of March 2023, the study included 60 patients with type 2 diabetes mellitus (30 males and 30 females). On the other hand, 30 people as a control group of both sexes (15 males and 15 females) were taken, and the ages of the two groups ranged between 30 and 65 years. The information about patients in this study was retrieved from the patients themselves through a direct interview with them, according to a prepared questionnaire. In the present study, blood samples were collected from each participant for estimation of vitamin D by (ELISA), HbA1c by (Cobas), lipid profile by (colorimetric methods) and calculated BMI. Results: The mean ± Standard Deviation (SD) of vitamin D levels for the type 2 diabetes group were (11.16± 2.18) ng /ml, with a highly significant decrease (p < 0.001) when compared with control group (20.73± 3.64) ng /ml. The mean ± SD of HbA1c level for the type 2 diabetes group was (8.88± 1.86) %, with a highly significant increase (p < 0.001) when compared with control (5.59 0.45) %. The mean ± SD of cholesterol, TG, and LDL-C levels for the type 2 diabetes group were (161.48± 21.70) mg/dl, (203.40± 8.16) mg/dl and (81.15± 21.62) mg/dl, respectively, with a highly significant increase (p < 0.001) when compared with the control group (105.77± 12.50) mg/dl, (191.73± 8.70) mg/dl, and (22.96± 13.38) mg/dl, respectively. The mean ± SD of HDL-C levels for the type 2 diabetes group was (39.66± 2.52) mg/dl and control (44.46± 4.82) mg/dl, with a highly significant decrease when compared with the control group. The mean ± SD of BMI for the type 2 diabetes group was (27.20± 4.25) and control (26.66± 2.30), respectively, with no significant difference (p < 0.05) when comparing the two groups. Conclusion: The current study concluded that Vitamin D levels showed a highly significant decrease in patients with uncontrolled type 2 diabetes mellitus when compared with those in the control group.