Pyostomatitis vegetans (PSV) is a rare disease characterized by pustules. The typical manifestations are “snail-track” lesions, which widely involve multiple parts of the oral mucosa. It is often associated with inflammatory bowel disease. This paper reports a case of a patients with PSV and unilateral circumscribed swelling. Ulcerative colitis was revealed by oral lesions. The clinical manifestations as well as histopathological and immunopathological features of PSV were analyzed and summarized to provide ideas for clinical diagnosis and treatment.