Abstract： Objective To investigate the effects of NG-nitro-L-arginine (L-NA) on pulmonary surfactant (PS) and pulmonary cells apoptosis in lipopolysaccharide (LPS) induced acute lung injury (ALI). Methods Twenty-four male Sprague-Dawley (SD) rats were randomly divided into three groups: control group, model group, L-NA group. Model of ALI was reproduced by injection of LPS 5 mg/kg via sublingual vein in model group and L-NA group. L-NA (20 mg/kg) was administered in L-NA group, while normal saline was administered in control group and model group 3 hours after LPS injection. The rats were sacrificed at 6 hours after LPS injection, and the lung tissue was obtained for measuring the expressions of pulmonary surfactant protein A (SP-A) mRNA by in situ hybridization (ISH) method; meanwhile, apoptosis rate was evaluated by flow cytometry; the expression of caspase-3 was evaluated by Western blotting analysis; Bcl-2 and Bax were evaluated respectively by immunohistochemisty (IHC). Results Compared with that of the control group, SP-A mRNA [absorbance (A) value] in the lung tissue was significantly decreased by LPS (0.071±0.017 vs. 0.113±0.021) in model group, apoptosis rate of pulmonary cells [(25.04±4.57)% vs. (11.37±3.08)%], caspase-3 protein expression (A value: 298.64±37.11 vs. 110.24±14.35) and Bax protein expression (A value: 0.145±0.011 vs. 0.076±0.010) were significantly increased, Bcl-2 protein expression (A value: 0.064±0.011 vs. 0.073±0.009) and Bcl-2/Bax (0.447±0.086 vs. 0.976±0.157) were decreased in model group (all P<0.01). L-NA was given at 3 hours after LPS administration, the expressions of SP-A mRNA (A value: 0.085±0.015) and Bcl-2 protein (A value: 0.070±0.087) increased markedly, compared with model group (P<0.01 and P<0.05), but there were no significant changes in the pulmonary cells apoptosis rate [(20.67±1.35)%], caspase-3 protein expression (A value: 268.75±42.56), Bax protein expression (A value: 0.142±0.012) and Bcl-2/Bax (0.498±0.069) between L-NA group and model group (all P>0.05). Conclusion L-NA had no effect on LPS-induced pulmonary cell apoptosis and had no effect on the expressions of caspase-3 and Bax, but L-NA can protect the lung from LPS-induced injury by up-regulating the expression of PS.