Background: Acute kidney injury (AKI) results in a disturbance of calcium homeostasis. The relationship between serum calcium level in AKI patients and its relation to adverse outcome in ICU hadn't been studied well. Aim of work: To determine the frequency and relation between hypocalcemia and ICU patients with acute kidney injury. Subjects and methods: This cohort study was carried on 108 patients with AKI who were admitted to medical ICU, Zagazig University Hospitals from January 2021 for a period of 6 months. We classified our patients into two groups according to presence of hypocalcemia with serum corrected calcium < 8.5 mg/dl. All patients were subjected to full medical history, clinical examination & routine investigations. Serum total corrected and ionized calcium, creatinine were assessed at (admission, 3rd, 7th day) and albumin level at 1st and 7th day. Clinical outcome was evaluated according to Acute Physiologic Assessment And Chronic Health Evaluation II (APACHE II score) in addition to calculation of ICU stay in days and mortality of those patients. Results: Hypocalcemic AKI patients were about 35% of all patients. A statistically significant increase in staging of AKI in hypocalcemic AKI patients than those with normocalcemic AKI. There was a statistically significant decrease in baseline and 7th day total and corrected calcium levels in hypocalcemic as compared to normocalcemic patients. Conclusion: Hypocalcemia is a prevalent complication in ICU patients with AKI, and this was associated with adverse outcome with increasing length of ICU stay, morbidity and mortality of those patients.