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Introduction: Postoperative Acute Kidney Injury (AKI) occurs as the consequence of intraoperative risk factors associated with cardiac surgery. Biochemical monitoring of patients undergoing cardiac surgery enables early detection of AKI. Serum albumin and Blood Urea Nitrogen (BUN): creatinine ratio serves as a simple tool for identifying increased risk of AKI. Aim:To determine serum albumin and the BUN: creatinine ratio as a predictive tool for AKI risk in patients undergoing cardiac surgery. Materials and Methods: The present prospective observational study was conducted at Cardio Thoracic super specialty unit of SRM Medical College Hospital and Research Centre, Chennai, Tamil Nadu, India, between July 2020 to March 2021. A total of 30 patients undergoing coronary artery bypass grafting in the age group between 40 to 70 years with normal serum creatinine levels were included. Preoperative and postoperative parameters such as urea, creatinine, total protein, serum albumin, BUN: creatinine ratio and estimated Glomerular Filtration Rate (eGFR) were calculated. Data were analysed statistically by Analysis of Variance (ANOVA) and Student's t-test. Results: In present study, 24 (80%) were males and 6 (20%) were females. The mean age of the male and female patients was 57±0.72 years and 55.3±0.81 years respectively. Mean BUN: creatinine ratio was decreased on day 1 (16±0.78) and day 3 (8.19±0.87) postoperative phase as compared to preoperative day (14±0.63). Compared with preoperative albumin (3.65±0.1 g/ dL), hypoalbuminaemia was found on first and third postoperative day, (3.07±0.05 and 3.04±0.05 g/dL) respectively. With Receiver Operating Characteristic (ROC) curve analysis, Area Under the Curve (AUC) for albumin and BUN: creatinine ratio was 0.72 and 0.67 which revealed the diagnostic sensitivity of 86% and 78% respectively. On day 3 postoperative eGFR fell by 12.5%, indicating a danger of kidney injury. Conclusion: Hypoalbuminaemia and BUN: Creatinine ratio are simple biochemical tools to predict AKI in postoperative phase after cardiac surgery.