To study the effects of oseltamivir on ACE2/Ang (1-7) /MasR axis, lung injury and inflammation in young mice with pneumonia. Methods Fifty SPF male SD pups were purchased from Guangzhou Genio Biotechnology Co., LTD., and 12 of the 50 healthy pups were randomly selected as the healthy group for control. The remaining 38 mice were modeled with influenza virus, and 2 mice died accidentally during the modeling. The 36 successfully modeled mice were divided into model group, oseltamivir group and control group by random number table method, with 12 mice in each group. Young mice in the healthy group and model group were routinely fed, and the young mice in the oseltamivir group were given 10mg/kg oseltamivir orally, once a day, for 5 days. Rats in control group were injected with azithromycin 75mg/mL once a day for 1 w. Results Compared with healthy group, the serum LEVELS of IL-6, IL-8, TNF-α and apoptosis rates in model group, oseltamivir group and control group were increased (P＜0.05), and the levels of IL-6, IL-8, TNF-α and apoptosis rates were decreased after oseltamivir intervention (P＜0.05). Compared with healthy group, FEF50, FEF75, MMF and PEF levels in model group were decreased (P＜0.05), and lung coefficient was increased (P＜0.05). After oseltamivir intervention, FEF50, FEF75, MMF and PEF levels were increased (P＜0.05), and lung coefficient was decreased (P＜0.05). The lung tissue structures of the mice were different. Compared with healthy group, the levels of ACE2, Ang (1-7) and MasR in model group, oseltamivir group, control group, inhibitor group, agonist group, agonist + oseltamivir group and inhibitor + oseltamivir group were decreased (P＜0.05), while the levels of ACE and Ang ⅱ were increased (P＜0.05). Compared with model group, the levels of ACE2, Ang (1-7) and MasR in oseltamivir group, control group, agonist group and agonist + oseltamivir group were increased (P＜0.05), while the levels of ACE and Ang Ⅱ were decreased (P＜0.05). The levels of ACE2, Ang (1-7) and MasR in inhibitor group were decreased (P＜0.05). The levels of ACE and Ang Ⅱ increased (P＜0.05). There was no significant difference between model group and inhibitor + oseltamivir group (P＞0.05). Compared with control group, the levels of ACE2, Ang (1-7) and MasR in oseltamivir group, agonist group and agonist + oseltamivir group were increased (P＜0.05), while the levels of ACE and Ang Ⅱ were decreased (P＜0.05). There was no significant difference between oseltamivir group and agonist group (P＞0.05). Compared with oseltamivir group, the levels of ACE2, Ang (1-7) and MasR in agonist + oseltamivir group were increased (P＜0.05), while the levels of ACE and Ang ⅱ were decreased (P＜0.05).Conclusion Oseltamivir improves lung function in young pneumonia mice by increasing ACE2 /Ang-(1-7) /Mas receptor axis and decreasing inflammatory factors