Abstract Background SBP is a condition that requires a high index of suspicion, rapid and accurate diagnosis in addition to prompt and effective therapy. It is also characterized by a high recurrence rate within one year of the 1st episode. Objective Evaluation of ascitic fluid procalcitonin as a possible diagnostic and prognostic marker for spontaneous bacterial peritonitis and to study its role in diagnosis of SBP with no increase in the neutrophil count (where neutrophils in the ascitic fluid are less than 250 per ccm while the culture is positive). Patients and Methods Study was conducted at Hepatology and Gastroenterology Department in Ahmed Maher Teaching Hospital and Internal Medicine Department in Ain Shams University from January 2019 till July 2019. Total number of 50 patients with cirrhotic ascites entered this study were divided into three groups: Group A (patient group): 20 patients with SBP as diagnosed by 250 neutrophils or greater per cmm of the ascitic fluid as present in the guidelines. Group B (patient group): 20 patients with criteria suggestive of SBP (abdominal pain, fever, liver function deterioration, leukocytosis in the CBC with no other localization for the infection), but shows neutrophil count in the ascitic fluid less than 250 i.e not diagnostic by itself. Only Patients with positive culture will be included in this group. Group C (control group): 10 patients with ascites,but no evidence of SBP (symptomatic or laboratory) as the control. Results Ascitic fluid procalcitonin level was statistically significant higher in both groups A&B (SBP group) than group C (non-SBP group). As regards Group A VS Group B+ Group C: The cutoff point is 520 (pg). Its sensitivity is 95%. Its specificity is 53.3%. The AUC is 0.633. The positive predictive value is 57.6%. The negative predictive value is 94.1%. Regarding Group B VS Group C: The cut-off point is 300 (pg). Its sensitivity is 85%. Its specificity is 70%. The AUC is 0.823. The positive predictive value is 85%. The negative predictive value is 70%. Conclusion Ascitic fluid procalcitonin had high sensitivity and specificity in diagnosis of SBP. Procalcitonin is valuable in diagnosis and prognosis of SBP. Procalcitonin is more useful as inflammatory marker than in infections