Generalized pustular psoriasis of pregnancy (GPPP) is a rare form of generalized pustular psoriasis that typically occurs in the third trimester of pregnancy. It is characterized by widespread coalescent sterile pustules and erythematous patches with systemic symptoms such as fever. Generalized pustular psoriasis of pregnancy (GPPP) may be confused with acute generalized exanthematous pustulosis (AGEP), which has similar clinical and histologic features. A 33-year old multigravida woman at 18 weeks of gestation presented with erythematous patches and pustules visited our clinic. She had history of systemic lupus erythematosus for a month and was taking a dose of hydroxychloroquine, aspirin and oral iron. The skin biopsy findings showed subepidermal bullous lesion containing neutrophils and upper dermal neutrophilic infiltrate. Under the suspicion of AGEP, she stopped her medicine and was treated with anti-histamine, systemic and topical steroid, but without improvement. Another skin biopsy was done and she was re-diagnosed as GPPP. Skin lesions improved after treatment with systemic cyclosporine and her symptoms resolved after delivery. We herein present an educational case of GPPP that misdiagnosed as AGEP.