OBJECTIVE: Spontaneous Bacterial Peritonitis (SBP) is one of the most serious liver cirrhosis with ascites complications. Vitamin D (Vit D) deficiency has been associated with a high risk of infection and mortality in cirrhotic patients. Herein, the assessment of Vit D level as a prognostic marker in SBP patients and the impact of Vit D supplementation on their treatment plan was studied as well. PATIENTS AND METHODS: Ascetic patients with SBP and Vit D deficiency were divided randomly into treatment and control groups. The control group received standard treatment without Vit D and the treatment group received standard treatment plus Vit D. Clinical monitoring of Vit D was done over 6 months. RESULTS: At baseline, all patients in both groups revealed an elevated serum and ascetic TLC, AST, ALT, total and direct bilirubin, in addition to elevation in INR and procalcitonin (PCT) level. Univariate regression analysis confirmed that deficiency of Vit D was an independent predictor of infection and mortality (p < 0.01; Crude Hazard Ratio: 0.951). Over 6 months, the study revealed significant improvement in serum Vit D level in the treatment group (34.6 ± 9.2 and 18.3 ± 10.0 ng/mL; p < 0.001). Moreover, a statistically significant increase in survival rate (64% vs. 42%; p < 0.05) and duration (199.5 days vs. 185.5 days; p < 0.05) were recorded as well. Univariate and multivariate regression analysis confirmed that Vit D supplementation was positively correlated to survival over 6 months (p < 0.001; Adjusted Hazard Ratio: 0.895). CONCLUSIONS: Vit D deficiency is prevalent in SBP cirrhotic patients and is used as an independent predictor of infection and death. Therefore, Vit D supplementation revealed improvement in their response to treatment.