Introduction: Diabetes mellitus is one of the most common chronic metabolic diseases in children and adolescents, which changes the cellular metabolism. Phosphorus is an essentialelement for metabolism. Early in the progression of diabetes, a paradoxical metabolic imbalance in inorganic phosphate (Pi) occurs that may lead to reduced high energy phosphate and tissue hypoxia. While low and high uncontrolled blood sugars can be easily recognized by clinical symptoms, low and high plasma inorganic phosphate remain unrecognizable. Therefore, we aimed to assess the association between hemoglobin A1c (HbA1c) with serum inorganic phosphate in diabetes. Aim: To study the changes in serum phosphorus levels with severity of DM as adjudged by HbAlc by investigating the following parameters in serum. 1. Blood glucose level (FBS & PPBS) 2. Glycated HbA1c 3. Serum Phosphorus. Materials And Methods: The present study involved 50 healthy controls and 50 clinically diagnoseddiabetic cases.Blood samples were collected under aseptic precautions from controls andcases. Relevant investigations were carried out and results interpreted for statistical evaluation. Results: The levels of serum phosphorus decreased in diabetic cases compared to healthy controls . Blood urea and serum creatinine levels were withinnormal limits in both controls and cases which are statistically not significant. Conclusion: It is concluded that decrease in serum phosphorus level is negativelycorrelated with glycated HbAlc , indicates that as the severity of diabetes increasesthere is a significant decrease in serum phosphorus level. Thereforediabeticstreatedwith insulin should be monitored to prevent morbidity and mortalityfromhypophosphatemia.