Objective To study the advantages of heat and moisture exchangers compared with heated humidifiers in reducing the incidence of ventilator-associated pneumonia ( VAP) . Methods We searched PubMed as well as reference lists from publications to collect randomized controlled trials which comparing heat and moisture exchangers with heated humidifiers in preventing VAP for mechanically ventilated patients. Meta-analysis was performed using software Review Manager 5. 0. Results Fifteen randomized controlled trials were included. There was no difference in incidence of VAP among the patients managed with moisture exchangers or heated humidifiers ( OR1. 18, 95% CI [ 0. 96, 1. 44] ) . The subgroup of patients using moisture exchangers had lower VAP incidence compared with those using heated humidifiers without heated wire circuits ( OR 1. 39, 95% CI [ 1. 08, 1. 79] ) . There were no differences between the compared groups in mortality, length of intensive care unit stay, or duration of mechanical ventilation. Conclusion The available evidence indicates that moisture exchangers are superior to heated humidifiers without heated wire circuits, and not to heated humidifiers with heated wire circuits to prevent VAP.