Objective: The purpose of the study is to observe the metformin associated effects on Vitamin B12 among Type II Diabetes mellitus patients. Methods: An observational study conducted over the period of 12 months on Type II Diabetes mellitus patients who are in the chronic therapy of metformin. The study described about the Vitamin B12 levels among the Type II DM patients which was able to alert the patients who are in the low and border range of Vitamin B12 to prevent the risk of peripheral neuropathic complications. Findings: Totally 102 patients were enrolled as per the inclusion and exclusion criteria, during the study total 61 males (59.8%) and 41 females (40.2%) were enrolled. Among them 12 patients (mean 49.16±S.D10.53) on low level of the Vitamin B12 followed by 16 patients (mean 51.95±S.D7.12) found to above the normal range of the Vitamin B12 followed by 30 (mean 57.53±S.D4.55) patients found to borderline of the Vitamin B12. Conclusion: High doses with chronic therapy of Metformin may alter Vitamin B12 level. Some of the patients had been observed abnormal level of higher value of Vitamin B12. In such Patients’ diet history also had some impact on Vitamin B12. However, the high chances of metformin associated effect on Vitamin B12 with higher doses of metformin with long term therapy. Moreover, age also important fact that the study reveals among gender, male population had higher rate of low level Vitamin B12 than female population. Moreover, Patients age group between 50 and 65(male58 ± 3.58, female 57.16±3.81) were having higher rate of low level Vitamin B12 than other age group. Patients with other comorbid condition also had low level and borderline of Vitamin B12 those who were on long term therapy of metformin. Therefore, our study concluding that chronic therapy of metformin may lead to deficit in serum Vitamin B12 which required regular check on Vitamin B12 among Type 2 DM patients to avoid the risk of Peripheral neuropathy and other complications.