Acute generalized exanthematous pustulosis (AGEP) is a rare disorder characterized by acute onset of erythematous and edematous eruptions with sterile pustules, accompanied by fever, and a self-limiting condition thought to be caused by drugs, in particular, antibiotics. Drug-related rash with eosinophilia and systemic symptoms (DRESS) syndrome is a severe adverse drug-induced reaction, characterized by a generalized skin rash associated with hypereosinophilia, lymphocytosis, and internal organ involvement. These reactions differ in causative agents, as well as clinical presentation, prognosis, and treatment. Therefore, appropriate diagnostic measures should be rapidly undertaken. Herein, we described a patient who developed overlapping features of hypersensitivity syndromes, AGEP and DRESS, with the use of piperacillin and the beta-lactamase inhibitor sodium tazobactam. Coexistence of AGEP and DRESS in the same patient is quite rare. To the best of our knowledge, there have been no previous reports on the coexistence of AGEP and DRESS associated with piperacillin/tazobactam.