Introduction: Blood transfusion is a life-saving procedure, but it has its own risks, both noninfectious and infectious complications. One packed RBCs unit believed to raise the levels of hemoglobin by 1 g per dl and hematocrit by 3 percent. Each patient should be dealt on an individual basis with assessment of the clinical signs and symptoms, in consideration to haemodynamic instability, comorbidity and the risk of further blood loss.Objective: 1.To study the change in hemoglobin level and hematocrit after the transfusion of single unit packed cell 2. To analyze any difference in rise in hemoglobulin and hematocrit based on age, gender and pretransfusion hemoglobulin concentration. Materials And Methods: The study is a retrospective study conducted in the blood bank of Chettinad hospital & research institute. All the recorded data for a period of 6 months from January 2019-June 20l9 were retrieved. All the patients, who were transfused single unit of packed cell with clinical details and other hemoglobin investigations in the study in our hospital, were included in the study. Patient without proper clinical and hematological investigation, neonates and children were excluded. Institutional ethical clearance was obtained before the commencement of the study. Statistical analysis was done using SPSS software and the results were expressed as mean and standard deviation. One way ANOVA test was performed between variables and a p value of <0.5 is considered significant. Results: During the study period 1289 transfusions were done in our hospital for various reasons. Of these 222 were single unit packed cell transfusions. The mean age is 48.05±16.48. The male: female ratio is 1.43. The mean rise in hemoglobulin and hematocrit in general, males and females are 1.04 & 2.84,