Objective: To determine the mean decrease in homocysteine levels in patient of type II diabetes mellitus on vitamin B12 therapy. Study design: A quasi experimental study. Place and Duration: In the Medicine Unit II of Services Hospital Lahore for Six months duration from July 2018 to January 2019. Methods: 72 total patients were selected for the study during the six-month study period. Blood samples were taken for fasting blood glucose and homocysteine to evaluate inclusion criteria at the beginning of the study. Patients were given vitamin B12 500 mg / day for 6 weeks. Fasting homocysteine levels were determined again after 6 weeks. To ensure that bias is minimized, sample collection, transport and laboratory procedures are standardized. Using SPSS version 20.0 data analysis was done. Results: The mean difference in homocysteine before and after treatment was 0.39 (95% CI 0.36 to 0.42) and a statistically significant p value of <0.001. Conclusion: It was concluded that vitamin B12 have an important role in decreasing levels of homocysteine in patients with type II diabetes. Key words: Homocysteine levels, vitamin B12, diabetes mellitus type II.