Objective To investigate the effect and its mechanism of vitamin A (VA) deficiency (VAD) on regulating alveolar macrophage polarization in neonatal rats with acute respiratory distress syndrome (ARDS). Methods Sixty neonatal SD rats were divided into vitamin A normal control group (VAN ctrl group, n=10), normal vitamin A group (VAN group, n=10), vitamin A deficiency control group (VAD ctrl group, n=10), vitamin A deficiency group (VAD group, n=10), vitamin A rescue control group (VADR ctrl group, n=10) and vitamin A rescue group (VADR group, n=10). The VADR ctrl and VADR groups were injected with 25 µg VA at the second day after birth. All the neonatal rats were given lipopolysaccharide (LPS) to establish the neonatal rat model of ARDS, and serum and lung tissue samples were collected. The weight of newborn rats in each group was recorded before modeling, the May-Grunwald-Giemsa staining was performed to observe the number of main cells in bronchoalveolar lavage fluid (BALF), and HE staining was used to detect the pathological damage of lung tissue. The polarization of alveolar macrophages was evaluated by immunofluorescence. qRT-PCR and ELISA were performed to detected the expression of downstream markers of the polarization of alveolar macrophages inducible nitric oxide synthase (iNOS), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), IL-10 and arginase-1 (Arg-1). The content of superoxide dismutase (SOD) and malondialdehyde (MDA) in lung tissue were calculated by colorimetric method, and cell apoptosis was detected by TUNEL. Results Compared with the neonatal rats in VAN group, the neonatal rats in VAD group had lower body weight, small physique, and sparse hair, while the body weight and general condition of the newborn rats in the VADR group did not change significantly. Compared with the VAD group, the neonatal rats in VADR group gained weight and shiny hair. Compared with VAN group, the lung damage of ARDS neonatal rats in VAD group was aggravated, the number of major cells in BALF increased, the M1 polarization of alveolar macrophages activated (P<0.05), the expression levels of M1 polarization markers iNOS, IL-6, TNF-α and CD86 increased significantly (P<0.05), the content of oxidative stress marker MDA and cell apoptosis increased (P<0.05), SOD activity decreased (P<0.05), while the levels of IL-10 and Arg-1 were not statistically significant (P>0.05); Compared with VAN group, there were no significant differences in macrophage M1 polarization, TNF-α, IL-6, SOD, MDA, IL-10 and Arg-1 in newborn rats in VADR group (P>0.05). Compared with VAD group, the lung damage of ARDS neonatal rats in VADR group was significantly reduced, the number of alveolar macrophages and the polarization of alveolar macrophages M1 decreased (P<0.05), the expression levels of M1 polarization markers iNOS, IL-6, TNF-α and CD86 decreased (P<0.05), the content of the oxidative stress marker MDA and cell apoptosis decreased (P<0.05), and the SOD activity enhanced (P<0.05). Conclusion VAD could regulate the M1 polarization of alveolar macrophages, up-regulated the expression of inflammatory markers downstream of M1 polarization, increased pulmonary oxidative stress and apoptosis, and aggravated ARDS in neonatal rats.