Aim: Periodontitis is an inflammatory disease causing destruction of tooth-supporting structures. It is often caused by gram-negative microorganisms such as Porphyromonas gingivalis (P. gingivalis). Common treatments for periodontitis are often nonspecific and include mechanical plaque removal and surgery. This study aimed to assess the amount of bone loss and antibody titer against P. gingivalis in rats. Materials and methods: This in vitro experimental study was conducted on 66 Surrey rats free of black pigmented pathogens, which were randomly divided into six groups of 11. Groups I and II were vaccinated with formalin-killed whole-cell (FKWC) P. gingivalis with incomplete Freund's adjuvant as the vaccine carrier, and groups III and IV were vaccinated with incomplete Freund's adjuvant and PG buffer. Groups V and VI were considered as positive and negative controls, respectively. Three weeks later, they were vaccinated with a booster dose. At 28 days, groups I, III, and V were inoculated with viable P. gingivalis (ATCC 33277) four times at 48-hour intervals for induction of periodontitis. One week after booster dose administration and two weeks after oral inoculation of bacteria, serum and saliva samples were obtained for assessment of antibody titer. Ten weeks after final bacterial inoculation, the serum and saliva samples were obtained to assess antibody titer, and subgingival plaque samples were obtained from the maxillary second molar site to assess the bacterial count. The rats were then sacrificed to assess bone loss. Results: Serum and saliva antibody titers in groups I and II were significantly different from those in other groups one week after booster dose and two and 10 weeks after oral inoculation of bacteria (p < 0.001). In terms of bone loss and bacterial count in the subgingival plaque, group I was not significantly different from the negative control group and groups II, IV, and VI (p > 0.99), but had a significant difference with the positive control (group V) and group III (p < 0.001). Conclusion: This study showed successful immunization against P. gingivalis, which increased serum IgG and saliva IgA titers, limited the colonization of P. gingivalis in subgingival plaque, and restricted the alveolar bone loss.