Objective To investigate the effects of mechanical ventilation on lung pathology and concentration of proinflammatory cytokines in rats.Methods Forty-five healthy Sprague-Dawley rats were randomly divided into three groups with 15 rats each group，ie.a control group(No mechanical ventilation)，a high tidal volume group(VT 34 mL/kg，RR 30 bpm) and low tidal volume group(VT 8 mL/kg，RR 60 bpm).Results There were enlarged alveolar spaces，interalveolar septum collapse，swollen and spotty hemorrhages，inflammatory cell infiltration in the ventilation groups，which was more serious in the high tidal volume group.Lung wet-to-dry weight ratio of high tidal volume group was significantly higher than that of other groups（both Plt;0.05）.The concentrations in both macrophage-inflammatory protein-2（MIP-2）and tumor necrosis factor-α(TNF-α) of bronchoalveolar lavage fluid(BALF) and blood samples was significantly higher in two ventilation groups than the control group（Plt;0.05），which were higer in the high tidal volume group than in the low tidal volume group（Plt;0.05）.Conclusions These results indicate that mechanical ventilation can cause lung injury，which is more serious in high tidal volume ventilation.And mechanical ventilation-induced lung injury can cause proinflammatory cytokines release，with different levels in bronchoalveolar lavage fluid and blood samples.