Porphyromonas gingivalis, a gram-negative anaerobic oral bacterium, causes periodontal disease by binding to saliva-coated oral surfaces. The FimA protein from P. gingivalis is a crucial pathogenic component of the bacterium and a target for vaccine development against periodontal disease. Complementary DNAs encoding the heavy and light chains of two monoclonal antibodies that bind specifically to the FimA protein were cloned into a plant expression vector under the control of the duplicated Cauliflower Mosaic Virus 35S promoter, and agroinfiltration was used to allow the vectors to infiltrate tobacco plants. The expressions of the heavy and light chains in the leaf tissue were detected using antibodies specific to each antibody chain. Western blot analysis showed the specific binding of the plant-derived monoclonal antibodies to the native FimA protein purified from P. gingivalis. Our finding that plant-derived monoclonal antibodies bound specifically to the native FimA protein indicates that plant-derived monoclonal antibodies can protect against P. gingivalis invasion.