Adverse drug reactions are very common in clinical practice, and skin is one of the most frequent organs for adverse drug reactions. We report a case of a 71-year-old male patient who developed skin eruptions after switching formulation of quetiapine immediate release(IR) to quetiapine extended release(XR). He had been taking quetiapine IR(400mg/day) for treatment of manic episode which was developed one year ago. The patient showed great improvement of symptoms after taking quetiapine IR for about one year, thus dosage of medication was reduced to 50mg/day on the average. Unfortunately dose reduction has tended to worsen symptoms, so dose of quetiapine was increased again to 200mg/day with formulation changes to XR. Two days after he took new formulation, erythematous papules were occurred over his anterior neck and ventral side of left wrist. As he stopped quetiapine XR, the skin lesions gradually subsided. And he was successfully treated with readministration of quetiapine IR without any skin lesions.