Background and study aim: Spontaneous bacterial peritonitis (SBP) is a serious complication of decompensated liver cirrhosis. It may be presented with atypical symptoms or asymptomatic, so ascitic fluid examination is recommended beside the clinical evaluation for the diagnosis of SBP. This study aimed to evaluate the value of macrophage inflammatory protein I (MIP I) and platelet indices as diagnostic markers for spontaneous bacterial peritonitis. Patients and Method: This is a cross-sectional study comprised 75 cirrhotic patients. Patients were divided into two groups according to the presence of ascites: group I: Comprising 50 cirrhotic patients with ascites who were classified into: group Ia comprising 25 patients with SBP, group Ib comprising 25 without SBP, and group II: Comprising 25 cirrhotic patients without ascites with other bacterial infections. All patients were subjected to history taking, full clinical examination, ultrasonographic examination; laboratory investigation (complete blood count (CBC), liver, and kidney function tests and serum C reactive protein (CRP)), Diagnostic paracentesis and ascetic fluid examination were done for all ascitic patients. Measurement of MIP I in serum and ascitic fluid was done. Results: significant increases in CRP, white blood cell count, mean platelet volume (MPV) and platelet distribution width (PDW), were found in SBP group compared to other groups (P<0.001). Serum MIP-1 level at a cut-off value >85 pg/ml could predict presence of SBP, with a sensitivity 100% and a specificity 44%. Ascitic MIP-I at a cut-off value of > 120 pg/ml could predict the presence of SBP with sensitivity 68% and specificity 100%. Cut-off value for MPV was (> 8.5 fl) could predict SBP presence, with sensitivity 76% and specificity 52%. Cut-off value for PDW was (> 15 fl) could predict SBP presence, with sensitivity 84% and specificity 84%. Conclusion: Serum and ascitic MIP-1β and platelets indices are useful diagnostic biomarkers for spontaneous bacterial peritonitis .