Abstract: Paradoxical psoriasis is a special adverse drug reaction characterized by the new onset, exacerbation, or phenotypic change of psoriatic lesions during treatment with biological agents. In recent years, with the increasing use of biologics, this condition has garnered growing attention from clinicians. The pathogenesis of paradoxical psoriasis is complex and its clinical manifestations are highly heterogeneous. Diagnosis currently relies primarily on clinical features and medication history due to the lack of unified diagnostic criteria. Furthermore, treatment strategies—such as whether to discontinue the original biologic agent or switch therapies—remain controversial, posing significant challenges in clinical management.This article presents a case of paradoxical psoriasis occurring in a patient with ankylosing spondylitis following treatment with the tumor necrosis factor-α inhibitor (TNFi) infliximab. By discussing the clinical characteristics of this case, we aim to enhance clinicians' understanding of this condition, reduce misdiagnosis and underdiagnosis, and provide valuable insights for its diagnosis and treatment.