Objective To investigate the effect of ambroxol pretreatment on the inflammatory response and lipid peroxidation during one-lung ventilation (OLV) .Methods Forty-five ASA I or II patients aged 37-64 yr weighing 53-65 kg undergoing thoracotomy under general anesthesia were randomly divided into 3 groups ( n = 15 each): group A two-lung ventilation (TLV); group B OLV and group C ambroxol 1 mg/kg + OLV. Anesthesia was induced with midazolam, fentanyl, propofol and atracurium and maintained with propofol infusion and intermittent iv boluses of fentanyl and atracurium. The patients were mechanically ventilated (VT8-10 ml/kg, RR 12 bpm during TLV, VT 6-7 ml/kg, RR 16 bpm during OLV, I: E 1:2, FiO2 100% ). In group C ambroxol 1 mg/kg in normal saline ( NS) 100 ml was infused at 25 min before OLV (infusion rate 4 ml/min) , while in group A and B equal volume of NS was infused instead of ambroxol. Blood samples were obtained from radial artery before induction of anesthesia and OLV (T0.1 ) and at 0.5, 1, 2 h of OLV (T2-4 ) and 1, 2 h of TLV (T5,6 ) and at 24 h after operation (T7) in group B and C for determination of serum SOD activity and TNF-α, IL-6 and IL-8 concentrations and WBC and neutrophil granulocyte counts. The same indexes were detected in group A at the corresponding time points.Results Serum SOD activity was significantly lower and serum TNF-α, IL-6 and IL-8 concentrations and WBC and neutrophil granulocyte counts were significantly higher in group B than in group A. Serum SOD activity was significantly higher and serum TNF-a, IL-6 and IL-8 concentrations and WBC and neutrophil granulocyte counts were significantly lower in group C than in group B. Conclusion Pretreatment with ambroxol 1 mg/kg can inhibit inflammatory response and lipid peroxidation during OLV.