Background/Objectives: Acute lung injury (ALI) is a respiratory disorder lacking specific targeted therapy. Our preliminary screening revealed that the ethanol extract of the seeds of Podocarpus nakaii (EESPN) alleviated the symptoms of ALI in mice. The objectives of this study were to identify the active constituents in EESPN and study the mechanism involved. Methods: Column chromatography was performed to separate the chemical constituents of EESPN. The structures of the isolates were determined via spectroscopic methods. MTT assays, Western blotting, histological analysis, TUNEL assays, immunofluorescence staining, transcriptomic analysis, and quantitative real-time polymerase chain reaction (qRT–PCR) were employed to evaluate the anti-inflammatory activity and to elucidate the potential mechanism of nagilactone C (3, Nag C) in ALI treatment. Results: Twelve compounds were isolated from EESPN and structurally characterized. The structure of podolactone E (1) was confirmed via single-crystal X-ray diffraction. In vitro, Nag C showed potent anti-inflammatory activity in LPS-induced RAW 264.7 cells. Nag C liposomes significantly ameliorated LPS-induced histopathological damage to the lungs, reduced neutrophil infiltration and inflammatory cytokine levels, increased myeloperoxidase (MPO) activity, and promoted apoptosis in mice. In addition to suppressing inflammation, Nag C also significantly suppressed the phosphorylation of the NF-κB, STAT3, and STAT1 proteins. Conclusions: Nag C is an active constituent of EESPN. It may protect against LPS-induced ALI via inhibition of the STAT signaling pathway. Thus, Nag C is a promising lead compound in the development of novel STAT-targeted anti-inflammatory agents.