Background: acute kidney injury (AKI) has arisen as a global public health problem and associated with high morbidity and mortality where the AKI mortality is more than 50%. It is a serious complication frequently occurred in ICU In hospitalized patients, 15% of them developed AKI and around 40% of AKI patients were referred to ICU. Objective: The aim of this study was to compare between effect of Sustained Low Efficiency Hemodialysis and Online Hemodiafiltration in Critically Ill patients with Acute Kidney Injury. Patients and Methods: This prospective study included a total of forty (age and sex matched) patients with Acute Kidney Injury (AKI) who were critically ill, attending at Nephrology Unit, Bab El-Shaareya, Al-Azhar University Hospitals. The patients were divided into 2 groups; Group (A): 20 patients on Sustained Low Efficiency Hemodialysis (SLED) and Group (B): 20 patients on Online Hemodiafiltration (OLHDF) Results: there was no significant difference between the two groups as regard Intradialytic hypotension (2 patients (10 %) in group 1 and 5 patients in group 2 (25%) p-value = 0.2). There was no significant difference between the two groups as regard weaning from ventilator (4 patients (40%) in group 1 and 3 patients in group 2 (42.8%) p-value = 0.5). Conclusion: Online haemodiafiltration (OL-HDF) showed to be better than IHD-LI in many aspects but there was no statistically significant difference in mortality, allowing us to recommend as first choice OL-HDF of treatment proposed for critically ill patients with acute kidney injury.