BackgroundProbiotic treatments might contribute to the prevention of ventilation-associated pneumonia (VAP). Due to its unclear clinical effects, here we intend to assess the preventive effect and safety of probiotics on Intensive Care Unit (ICU) patients.MethodsEligible randomised controlled trials were selected in databases until 31 September 2019. The characteristics of the studies were extracted, including study design, definition of VAP, probiotics intervention, category of included patients, incidence of VAP, mortality, duration of mechanical ventilation(MV) and ICU stay. Heterogeneity was evaluated by Chi-square and I2 tests.Results15 studies involving 2039 patients were identified for analysis. The pooled analysis suggests significant reduction on VAP (RR, 0.68; 95%Cl, 0.60 to 0.77; p<0.00001) in a fixed effect model. And subgroup analysis was performed on category of clinical and microbiogical criteria both support the above conclusion. However, no significant difference in duration of MV or length of ICU stay in a random effect model. Also, no significant differences in total mortality, overall mortality, 28-day mortality, 90-day mortality were found in the fixed effect model.ConclusionsThe probiotics helped prevent VAP without impacting duration of mechanical ventilation, length of ICU stay, or mortality.