BACKGROUND: Periodic fever, aphthous stomatitis, pharyngitis, and cervical adenitis (PFAPA) syndrome has been considered as a childhood syndrome. Its etiopathogeny is unknown however, currently considered as auto-immune inflammatory disease. Recently, a few cases of adult-onset of PFAPA syndrome have been reported. However, there is no report about the adult-onset of PFAPA case with a novel TNFAIP3 Mutation. OBJECTIVE AND METHOD: Followed by detailed clinical inquiry, related laboratory tests, genetic sequencing and treatment, we reported a case with the adult-onset of PFAPA syndrome with a novel TNFAIP3 mutation. RESULTS: We have found a novel mutation in the gene TNFAIP3 in an adult patient with periodic fever, aphthous stomatitis, pharyngitis, and adenitis-the PFAPA syndrome, under the environmental factor-COVID-19 vaccination. CONCLUSION: This case demonstrated adult-onset of PFAPA symptoms, including periodic fever of unknown origin, which can occur in adult patients with the familial hereditary TNFAIP3 mutation and environmental factors. And the therapeutic measures provide some reference and practical significance for the treatment of PFAPA syndrome.