Objective To investigate the effects of dexmedetomidine on apoptosis and CHOP in lung injury following one lung ventilation in SD rats.Methods 60 SD rats were randomly divided into the control group,OLV combined with 0.9%sodium chloride injection,and OLV combined with dexmedetomidine group with 20 rats in each group.The rats were killed after the detection of apoptosis index,and the proportion of wet and dry GRP78 and CHOP protein and gene expression level.Results Fluorescence microscope observed cell shrinkage,increased cytoplasmic density,mitochondrial membrane potential disappearance, permeability changes.Vesicular membrane had formed, membrane integrity,and could be wrapped apoptosis remains divided into several apoptotic bodies.3 groups apoptotic index,the proportion of wet and dry lung tissue had statistically significant differences ( F=9.675,4.357,all P<0.05).The apoptosis index of OLV combined 0.9%sodium chloride injection group and OLV combined with dexme-detomidine group,the proportion was higher wet lung tissue,OLV combined 0.9% sodium chloride injection group was higher than the OLV combined with dexmedetomidine group, the differences were statistically significant ( t =4.432,3.458,all P<0.05).3 group GRP78 protein,GRP78mRNA,CHOP protein,CHOPmRNA levels had statisti-cally significant differences(F=4.350,5.897,5.875,6.785,all P<0.05),OLV combined 0.9% sodium chloride injection group and OLV combined with dexmedetomidine group GRP78 protein, GRP78mRNA, CHOP protein, CHOPmRNA were higher than those in the control group,OLV combined 0.9%sodium chloride injection group was higher than the OLV combined with dexmedetomidine group,the difference was statistically significant(P<0.05). Conclusion Dexmedetomidine given OLV can induce apoptosis and reduce the expression levels of CHOP,indicating damage to the lungs caused by a protective effect OLV.