Type 2 diabetes, formerly known as adult-onset diabetes, is a form of diabetes mellitus that is characterized by high blood sugar, insulin resistance and relative lack of insulin. This cross sectional study was carried out in the Department of Biochemistry, Mymensingh Medical College and in collaboration with the Department of Endocrinology, Mymensingh Medical College Hospital, Mymensingh from July 2021 to June 2022. A total of 100 subjects were included in this study. Among them 50 were diagnosed type 2 diabetes mellitus patients denoted as case group and 50 were apparently healthy individuals denoted as control group selected on the basis of inclusion and exclusion criteria. Serum vitamin D was estimated by chemiluminescence immunoassay from the subjects. Data were then processed and analyzed. Statistical analysis was done by using SPSS (Statistical Package for Social Science) version 26 windows package. The study revealed that, mean±SD values of vitamin-D were 25.50±3.63 ng/ml and 27.72±5.25 ng/ml in Group I and Group II respectively. Student's unpaired 't' test was done to measure the level of significance. Serum vitamin-D was significantly lower in Group I than that of Group II. This result has an association with type 2 diabetes mellitus progression and also may has important role in the etiology of type 2 diabetes mellitus and its complications.