Objective: To find the correlation of serum magnesium levels in diabetic patients with and without retinopathy.Methods: Hospital Based Cross-Sectional studywas conducted on diabetic patients who attend the ophthalmology outpatient department in a medical college and hospital, Puducherry. Patients were divided into two groups with and without diabetic retinopathy. After obtaining institutional ethical committee approval and consent from the patient, anthropometry measurements were taken, followed by the comparison of serum magnesium level estimation in both groups. All parameters are presented as mean±standard deviation (mean±SD). The data was entered and analysed by using Epi info (version 6.04d) software package. Results: The mean (SD) value of serum magnesium was 1.14 (0.17) and 1.42 (0.15), in cases and controls, respectively. Our results showed that the serum magnesium levels were significantly decreased (p<0.05) among patients with diabetic retinopathy as compared to patients without diabetic retinopathy.Conclusion: The strong association between serum magnesium levels and severity of type II Diabetes mellitus indicates a role for early prediction and appropriate therapeutic modifications to avoid end-stage disease complications.