Background: In patients with cirrhosis, spontaneous bacterial peritonitis is the most common bacterial infection. This research aims at studying the ascititc fluid Micro RNA-155 as a possible biomarker in spontaneous peritonitis. Method: 187 liver cirrhosis and ascites were chosen, 97 SBP patients and 90 SBP patients, all patients had historical history, thorough and local examination, comprehensive investigations, abdominal ultrasonography, diagnostic abdominal paracentesis and Micro RNA-155 evaluation. Results: in SBP, the average value of TLC, Polymorphene, and RNA-155 was considerably greater than non SBP, but in the SBP group the average value of ascetic albumin, glucose, and protein was considerably lower than in the non-SBP group. For MiR-155, the optimal balance of sensitivity and specificity was 0.022 for ROC as a marker with sensitivity 60 percent and specificity 62.0 percent and surface area under curve 0.639. No statistically significant link exists among SBP patients among Micro RNA-155 with TLC, polymorphs, MELD score and Child Pugh score values. Conclusion; Although MiR-155 was increased in the ascetic fluid of SBP patients, and is a predictor for SBP development, it cannot be employed as diagnostic marker in the SBP, according to this research.