Objective:To observe the changes of the cytokines and oxidative free radical, respiratory index and lung compliance during open heart surgery under cardiopulmonary bypass(CPB), and to investigate the protective effect of ulinastatin on pulmonary function simutaneously. Methods: Thirty patients undergoing elective valvular replacement were prospectively randomized into two groups: group U(n=15) with ulinastatin and group C(n=15)with physiological saline. The tumor necrosis factor-a (TNF-α)、interleukin-6(IL-6)、interleukin-8(IL-8)and Malonaldehyde Acetal (MDA) were assessed before CPB (T 1), 30 min following aortic clamping(T 2), 1hour(T 3), 2hours(T 4) and 3hours(T 5) reperfusion respectively. While pulmonary thoracic compliance (Cs) and dynamic compliance (Cd) were measured at T 1, T 3,T 4, T 5. Respiratory indexes (RI)were calculated at the same time. Results: There were no differences in the values of TNF-α, IL-6, IL-8, MDA, Cs, Cd and RI at T 1(base value) between the two groups (P>0.05). After CPB, the levels in both groups increased significantly as compared with T 1(P<0.01). The levels in the group U were lower significantly (P<0.05) at the time of T 2,T 3,T 4 and T 5 than those in control group. There was a significant (P<0.01) decrease of C s and C d at T 3,T 4,T 5 in control group as compared with base values (T 1) and the values of the group U respectively(P<0.05). The RI of the control group at T 3,T 4,T 5 were higher than both the base values and the values of group U respectively(P<0.05). Conclusion: CPB induces lung inflammatory injury,the pathophysiological changes lead to the increase of RI and the decrease of lung compliance. Ulinastatin could protect the lung injury from CPB by inhibiting the lung inflammatory injury.