Objective To investigate the effect of astragaloside on the TLR4-p38 MAPK signaling pathway in a newborn mouse acute lung injury model. Methods Seven-day-old SD newborn rats were used as experimental subjects. The model of acute lung injury in newborn rats was established by intraperitoneal lipopolysaccharide ( LPS) injection. Dexamethasone was used as a positive control. Each rat was injected intraperitoneally with 10 mL/ kg astragaloside. The lung lesions were observed 12 and 24 h after LPS injection. Furthermore, the mRNA and protein expression levels of TLR4 were determined, as well as the phosphorylation level of p38 protein. Finally, the changes in inflammatory factors TNF-α, IL-6 and IL-12 were analyzed. Results The model group showed pulmonary hemorrhage and a large number of collapsed alveoli at 12 h, and pulmonary edema and a significantly widened alveolar septum at 24 h after LPS injection. Compared with the model group, the lesions in the lung tissue of the astragaloside group were significantly alleviated. Additionally, Western blot result showed the levels of TLR4 (P< 0. 05) and p-p38 (P< 0. 001) were significantly lower in the astragaloside group than in the model group. The qPCR result showed that the level of TLR4 mRNA in the astragaloside group was significantly decreased compared with that in the model group (P< 0. 05). The inflammatory factors, TNF-α, IL-6 and IL- 12, were all decreased, and the relative IL-12 expression was significantly different from that in the model group (P< 0. 05). Conclusions Astragaloside plays an important role in alleviating the acute lung injury model of newborn rats by inhibiting the TLR4-p38 MAPK signaling pathway.