Introduction: Diabetes mellitus has increased incidence because of changing pattern of dietary and life style changes and stress. This metabolic disorder is associated with altered serum electrolyte levels like magnesium which may lead to serious complications if not detected early. Objective: To estimate and compare serum magnesium levels in uncontrolled and controlled diabetic groups. Materials and Methods:The study was conducted on 30 uncontrolled diabetic subjects with glycated haemoglobin (HbA₁ c) more than 7 and 30 controlled diabetic subjects with good glycemic control, HbA₁ c less than 7. Serum magnesium levels were estimated in both the groups. Statistical analysis was done by using Graphpad Quickcalcs calculator. Student's unpaired t-test was done to compare between two groups and statistical significance was determined and expressed as P-value. Results:Serum magnesium levels expressed as mean ±  S.D. was 1.440± 0.271 in uncontrolled diabetic group when compared to 2.033 ± 0.385 in controlled diabetic group. The decrease in serum magnesium levels in poorly controlled diabetics than in those diabetics with good glycemic control has a p-value < 0.0001 which is of extreme statistical significance. Conclusion:To conclude there was decreased serum magnesium in uncontrolled diabetics when compared to well controlled diabetics. This warrants the need for correction of hypomagnesemia in diabetics to prevent associated complications and morbidity.