Background: Cirrhosis is the main cause of ascites, where it indicates poor prognosis with approximately 50% mortality at 2 years. The risk is increased with other complications including spontaneous bacterial peritonitis (SBP). Procalcitonin (PCT) is a significant marker for sepsis because its level is usually high in septic conditions but remains low in nonspecific inflammatory diseases and viral infections. Objective: To assess the impact of serum and ascitic fluid procalcitonin on diagnosis and optimization of antibiotic therapy in SBP in cirrhotic patients. Patients and Methods: 55 patients with liver cirrhosis and ascites, 25 of them suffered from SBP and the other 30 patients free from bacterial infection were enrolled in the study. All patients were subjected to full history, examination and assessment for serum and ascitic fluid procalcitonin. Results: The median age was 60.4±10.2 years in the SBP and 61.3±10.6 years in non SBP patients. There was no statistically significant difference between non SBP and SBP groups regarding their age, sex and diabetes meelitus (DM) frequency. Ascitic fluid culture was done to the SBP group where 3 cases were sensitive to ciprofloxacin, one case sensitive to amikacin and 1 case sensitive to meropenem and one case sensitive to vancomycin. A statistically significant higher median ascitic fluid and serum PCT was found among SBP than non SBP group. with every increase one unit increases risk of SBP by 1.01 (Odds ratio= 1.01, 95% CI: 1.0 -1.01). The overall percent predicted was 87.3%. Conclusion: PCT was significantly high in the serum and ascitic fluid of SBP patients with high specificity, sensitivity, positive and negative predictive value. Ascitic fluid analysis with polymorphonuclear leukocyte (PMN) count remains the standard key to diagnose SBP.