Objective To investigate the effects of different blood pH of the recipients on ischemiareperfusion (I/R) injury to the transplanted lungs in rats. Methods Sixty-four pure bred male SD rats weighing 250-350 g were randomly divided into equal numbers of donors and recipients and the recipient rats were randomly divided into 4 groups(n = 8 each). Both donor and recipient rats were anesthetized with intraperitoneal (IP)ketamine 15 mg/kg and diazepam 6 mg/kg, tracheostomized and mechanically ventilated. In donor rats heparin 1 ml was injected via inferior vena cava and 4 ℃ LDP solution 40 ml was injected via pulmonary artery . The left lung was then removed and placed in 4℃ LDP solution and kept for 4 h. The left lung transplantation was performed using two-cuff-one-stent anastomosis technique. Before the transplanted lung was reperfused, the recipients' blood pH was adjusted to 7.4 (group Ⅰ), 7.2 (group Ⅱ), 7.3 (group Ⅲ) and 7.5 (group Ⅳ) by HCI and NaHCO3 solutions infused via femoral vein. After 2 h reperfusion, the transplants were removed for microscopic examination and determination of W/D lung weight ratio, MPO and SOD activities and MDA, TNF-α and IL-8 contents. Results SOD activity was significantly higher while MPO activity, and MDA, TNF-α and IL-8 contents in the lung tissue were significantly lower in group Ⅲ than in group Ⅰ . There was no significant difference in SOD and MPO activities and MDA, TNF-α, and IL-8 contents in the lung tissue among group Ⅰ , Ⅱ and Ⅳ. There was no significant difference in W/D lung weight ratio among the 4 groups. Microscopic examination showed that the histological damage was attenuated in group Ⅲ compared with the other 3 groups. Conclusion The I/R injury to the transplanted rat lungs can be effectively alleviated by reducing blood pH of the recipients to 7.3.