Background: Spontaneous bacterial peritonitis (SBP) is a severe complication of cirrhotic ascites. SBP diagnosis is based on the count of ascitic fluid neutrophils (>250/mm³). This procedure is an invasive maneuver with many complications. This study aimed to find a sensitive diagnostic tool for SBP by examining ascitic fluid Macrophage Inflammatory Protein type 1 beta(MIP-1β) as a rapid bedside test for diagnosis of SBP. Materials and methods: The study included 53 cirrhotic ascitic patients (33 with and 20 without SBP). Patients were subjected to thorough medical history taking, clinical examination, and laboratory investigation. Two ascitic fluid samples were taken, the first at admission time for cell count and culture, and the second sample was taken 48 hours after treatment in patients with SBP. Ascitic MIP-1β was measured using ELISA technique at admission in both groups and 48 hours after treatment in the SBP group. Results: Ascitic MIP-1β and CRP levels were significantly higher in the SBP group versus non-SBP patients. There was a significant positive correlation between ascitic fluid MIP-1β and WBCs and serum CRP. Ascitic fluid MIP-1β at a cut-off value ≥ of 31.95 pg/ml had 79% sensitivity and 75% specificity for the diagnosis of SBP. Combined ascetic fluid MIP-1β at the cut-off value ≥31.95 pg/ml and CRP in serum at a cut-off value ≥of 36 mg/L had 61% sensitivity and 100% specificity. There was a significant decrease of both, ascitic MIP-1β and ascetic fluid PMN after treatment of SBP. Conclusions: Ascitic fluid MIP-1β is highly sensitive and specific in the diagnosis of SBP- especially when combined with CRP.