Aim: This study was to observe the changes of the gene expression of microRNA-155 and 127 in the neonatal rats with Acute Lung Injury (ALI). Methods: Eighty neonatal SD rats were randomly divided into experimental groups (intraperitoneal injection with LPS, n=60) and control (intraperitoneal injection with NS, n=20). Neonatal rats in experimental groups (LPS 1 mg, 2 mg and 3 mg group, n=20) were received corresponding dose of LPS (1, 2 and 3 mg/kg, diluted with saline to 0.2 ml), while neonatal rats in control group were injected 0.2 ml saline respectively. Then we killed rats at 1 h, 6 h, 12 h and 24 h respectively in each group. The lung general pathological changes were observed. The expression of microRNA-155 and 127 were detected by semi-quantitative reverse transcription-polymerase chain reaction. Tumor Necrosis Factor-α (TNF-α) and Interleukelin-6 (IL-6) in Bronchoalveolar Lavage Fluid (BALF) were detected by enzyme-linked immunosorbent assay. The expression of TNF-α and IL-6 protein in lung tissue were detected by western blotting. Results: The expression of microRNA-155 was up-regulated in the tissues and BALF in a dose and timedependent manner and microRNA-127 down-regulated. The difference were statistically significant when compared with the control group (all P<0.05). The TNF-α and IL-6 level of BALF rats with ALI in LPS groups were increased compared with the control group in a dose-dependent manner (all P<0.05). A similar trend had been seen in TNF-α and IL-6 protein level of lung tissues, the difference was statistically significant. Conclusion: The expression of microRNA-155 and 127 are associated with severity of the ALI in a dose and time-dependent manner, and they might be considered as potential biomarkers for early diagnosis of ALI.