Periodontitis is an inflammatory condition of the oral cavity caused by a mixed infection of various bacteria, which not only severely affects the alveolar bone and connective tissues but also displays potential correlations with distal intestinal inflammation. In this study, we aimed to elucidate the therapeutic effects of Streptococcus cristatus CA119 on experimental periodontitis in rats and its impact on intestinal morphology. The results demonstrate that CA119 is capable of colonizing the oral cavity and exerting antagonistic effects on Porphyromonas gingivalis and Fusobacterium nucleatum, thus leading to a significant reduction in the oral pathogen load. Following CA119 intervention, there was a significant alleviation of weight loss in rats induced by periodontitis (P < 0.001). CA119 also regulated the expression of IL-6 (P < 0.05), IL-1β (P < 0.001), IL-18 (P < 0.001), COX-2 (P < 0.001), iNOS (P < 0.001), and MCP-1 (P < 0.01) in the gingival tissue. Additionally, CA119 reduced oxidative stress levels in rats and enhanced their antioxidant capacity. Microcomputed tomography (micro-CT) and histological analysis revealed that CA119 significantly reduced alveolar bone loss and reversed the downregulation of OPG/RANKL (P < 0.001). Furthermore, CA119 exhibited a significant protective effect against intestinal inflammation induced by periodontal disease and improved the colonic morphology in rats. In conclusion, this study demonstrates the role of CA119 as a potential oral probiotic in the prevention and treatment of experimental periodontitis, underscoring the potential of probiotics as a complementary approach to traditional periodontal care.