Introduction Spontaneous bacterial peritonitis (SBP) is a common infection in patients with hepatitis B virus (HBV)-related acute-on-chronic liver failure (ACLF). SBP significantly increases the mortality rate and medical costs. The association between proton pump inhibitor (PPI) use and SBP remains unclear. We conducted a retrospective study to investigate the association between PPI use and SBP in patients with HBV-related ACLF and to explore the risk factors for SBP. Methods We compared the SBP incidence between the PPI and non-PPI groups before and after propensity score matching and explored the association between the duration and type of PPI and SBP occurrence. Risk factors for SBP occurrence were determined by univariate and multivariate logistic regression analysis. Results The SBP incidence was higher in the PPI group than in the non-PPI group before and after propensity score matching. The SBP incidence increased for elevated MELD scores in PPI users. There was a similar SBP incidence in both different types and durations of PPI users. MELD score, old age, male sex, and high WBC count were significant independent risk factors for SBP in PPI users with HBV-related ACLF in the hospital. Conclusions PPI therapy increases the risk of SBP development in patients with HBV-related ACLF. MELD score, old age, male sex, and high WBC count could serve as predictors of SBP in PPI users. Caution should be taken regarding PPI use, especially for patients with MELD scores > 30.