Bacterial infection is frequently observed in patients with alcoholic liver disease (ALD). We examined a possible role of Porphyromonas gingivalis in the development/progression and severity of disease in patients with acute alcoholic hepatitis (AAH). Plasma specimens from 47 patients with AAH (16 moderate, Model for End-Stage Liver Disease [MELD] score <20]; 31 severe, MELD score >20) and 22 healthy controls (HCs) were collected. Clinical, drinking history (lifetime drinking history [LTDH]), and demographic data were collected. Antibody tests for immunoglobulin (Ig) G, IgM, and IgA against two P. gingivalis strains were performed. Between-group comparisons and within-group association analyses were carried out. Patients with severe AAH showed significantly higher plasma levels of IgG, IgA, and IgM against two P. gingivalis strains (W83 and 33277) compared to HCs. Patients with moderate AAH also had significantly elevated anti-P. gingivalis IgA concentrations for both strains compared to HCs. Male patients with moderate AAH showed a significant inverse association in LTDH and anti-P. gingivalis IgM. The aspartate aminotransferase:alanine aminotransferase ratio was positively associated with IgM of both strains in male patients with moderate AAH. Female patients with severe AAH showed a significant association between MELD scores and W83 IgM. Conclusion: Antibody response to P. gingivalis in AAH is elevated. Significantly elevated plasma anti-P. gingivalis IgG, IgA, and IgM in severe AAH provide preliminary data that P. gingivalis could be a novel risk factor in the development/severity of AAH.