Background and study aim: The most common infection in decompensated hepatic patients with cirrhotic ascites is spontaneous bacterial peritonitis (SBP), which occurs in the absence of an evident intra-abdominal source of infection. The aim of this work is to assess the value of calprotectin in ascitic fluid in diagnosis of spontaneous bacterial peritonitis in patients with liver cirrhosis. Patients and Methods: In this cross section study, 80 cirrhotic patients were divided into (group A) 40 patients with non SBP and (group B) 40 patients with SBP, who attended the Hepatology Department Benha University Hospital. All the patients were evaluated by thorough history, clinical examination, laboratory investigations, ultrasonography and diagnostic paracentesis with PMNs count and calprotectin which was measured in 1 mL ascetic fluid by ELISA. Results: Calprotectin was high in SBP group with a highly statistical significant difference in SBP group compared to non SBP group. The sensitivity of the test was 90% with specificity of 62.5%, PPV of 70.5% and NPV of 86.5% with the cut-off level were 2.98 ng /ml and the area under the curve was 0.88. It could serve as a sensitive and specific diagnostic test for detection of SBP in cirrhotic patients with ascites but many studies should be done on large numbers of patients to detect the accurate cut-off value. Conclusion: Ascitic calprotectin reliably predicts PMN count more than 250/ mm3, which may prove usefulness in the diagnosis of SBP.