Periodontitis is an inflammatory disease initiated by periodontopathogenic bacteria in the dental plaque biofilms. Understanding the role ofPorphyromonas gingivalis(P. gingivalis), a keystone pathogen associated with chronic periodontitis, in the inflammatory response is crucial. Herein, we investigated whetherP. gingivalisinfection triggers the expression of the type I IFN gene and various cytokines and leads to activation of the cGAMP synthase–stimulator of IFN genes (cGAS-STING) pathway bothin vitroand in a mouse model. Additionally, in an experimental model of periodontitis usingP. gingivalis, StingGtmice showed lower levels of inflammatory cytokines and bone resorption than wild-type mice. Furthermore, we report that a STING inhibitor (SN-011) significantly decreased inflammatory cytokine production and osteoclast formation in a periodontitis mouse model withP. gingivalis. In addition, STING agonist (SR-717) -treated periodontitis mice displayed enhanced macrophage infiltration and M1 macrophage polarization in periodontal lesions compared with that in vehicle-treated periodontitis mice. In conclusion, our results demonstrate that the cGAS-STING signaling pathway may be one of the key mechanisms crucial for theP. gingivalis-induced inflammatory response that leads to chronic periodontitis.