Aims and Objective: The world today is witnessing epidemic of Diabetes Mellitus. It is a chronic disorder with multiorgan involvement. The aim of the present study 25(OH) Vitamin D3 as a causative factor in pathogenesis of type 2 diabetes Mellitus. Material and Methods: The present study was undertaken in the Department of General Medicine, RIMS, Ranchi. A total of 100 patients with Type 2 DM were included in the study and 40 controls were included. The quantitative determination of Vitamin D in human serum and plama was done using Chemiluminescent microparticle immunoassay (CMIA) with a flexible assay protocols, reffered as Chemiflex. Results: Of the total 100 cases 62(62%) were males and 38(38%) cases were female .Out of the total 100 cases 98(98%) were Vitamin D deficient and among controls out 0f 40 , 36(90%) were Vitamin D deficient. There was a negative correlation of serum Vitamin D level with FBS (r= -0.339). Conclusion: The general population is deficient in serum Vitamin D level and in diabetes mellitus patients it is still lower than the non diabetic control group. In view of the high incidence of Vitamin D deficiency across general population a long term follow up involving large number of patients is necessary to substantiate the relationship between Vitamin D deficiency in diabetes mellitus