Abstract： Objective To observe the expression of high mobility group box 1 (HMGB1)in the lung protection of oxygen controlled reperfusion against ischemia-reperfusion (I/R) with cardiopulmonary bypass (CPB) in canine. Methods Fourteen healthy canines were randomly divided into two groups:control group (n=7) and test group (n=7), and received CPB. The animals in the control group received 80% FiO2 throughout the whole procedure, whereas those in the test group received 40% immediately at the declamping of aorta, and an additional 10% every 5 min later until 80% FiO2 was reached. Other procedures were the same with control group. Arterial oxygen partial pressure (PaO2) was recorded after anesthesia was completed, before and at 5, 10, 15, 20, 25 min after sternotomy, and before withdrawal of CPB. HMGB1 expression by RT-PCR and Western blot, NF-κB expression by Western blot, IL-6 and TNF-α by ELISA were analyzed just after sternotomy(T1 ), 25 min after declamping(T2) and 90 min after declamping(T3). At the same time points, malondialdehyde, myeloperoxidase activity, wet/dry mass (Mw/MD) gnd tissue pathology were analyzed. Results PaO2 was significantly lower in the test group than that in the control group at 5, 10, 15 and 20 min after aortic declamping (all P＜0.05). Compared with the control group at T2 and T3, the test group was found to have lower levels in HMGB1 mRNA and protein expressions (T2:0.926 0±0.013 9 vs 1.049 6±0.030 6;T3:0.832 5±0.015 4 vs 0.989 4±0.014 4, both P＜0.05; T2:0.434 5±0.074 8 vs 0.551 2±0.047 4;T3:0.449 0±0.054 1vs 0.545 5±0.040 6, both P＜0.05), NF-κB protein expression in the lung tissues, IL-6 and TNF-α in serum, Mw/MD ratio, MDA level and MPO activity (all P＜0.05).Pathological scores in test group at T2 and T3 were significantly lower than those in control group (T2:2.0±0.7vs 3.8 ±0.5; T3:2.6±0.6 vs 4.2 ±0.8, both P＜0.05). Conclusion Oxygen controlled reperfusion possesses lung protection in early stage of I/R injury with CPB, which may be related to its inhibition of HMGB1 expression.