We evaluated the antibacterial, anti-inflammatory, and inhibitory effect of osteoclast differentiation of Brachypodium sylvaticum (BS) to find out the possibility of preventing periodontal disease. The inhibition of Porphyromonas gingivalis (P. gingivalis) growth by BS and the sustainability of the antibacterial activity was assessed. The production of pro-inflammatory cytokines from lipopolysaccharide (LPS)-induced RAW 264.7 cells were measured using enzyme-linked immunosorbent assays (ELISA), and the production of nitric oxide (NO) and cell viability were measured. Osteoclast differentiation was evaluated by Tartrate-resistant acid phosphatase (TRAP) staining, and TRAP activity. BS showed significant antibacterial activity and sustainable antibacterial activity in P. gingivalis. We also found out that the BS significantly decreased secretion of pro-inflammatory cytokines [tumor necrosis factor (TNF-α) and interleukin-6 (IL-6)] and NO production without cytotoxicity. Furthermore, BS inhibited the differentiation of bone marrow macrophages (BMMs) obtained from mouse bone marrow cells into osteoclasts without cytotoxicity. Taken together, BS can be a promising candidate for a preventive and improving agent of periodontal disease having antibacterial, anti-inflammatory, and inhibitory effects of osteoclast differentiation.