Authors report a case of hypertension associated with venlafaxine administration. A 52 years-old male patient with bipolar I disorder was hospitalized due to recently developed depressive symptoms. According to his past medical history, he had essential hypertension, which had been well controlled by intermittent antihypertensive therapy. He had no antihypertensive therapy for the last 3 years but maintained normal blood pressure. We started venlafaxine administration for his depressive symptoms and, after 9 days of venlafaxine administration, his blood pressure was abruptly elevated with nausea and headache at a dosage of 112.5mg/day. On 12th hospital day, this medication was adjusted up to 150mg/day. He showed no response to some conventional antihypertensive medications which had been effective for him. We thought that he had a hypertension associated with venlafaxine administration and decided to discontinue this medication. All the symptoms of elevated blood pressure, nausea and headache rapidly improved 4 days after stopping venlafaxine administration. It is necessary to assess blood pressure regularly in patients especially with past history of hypertension who take venlafaxine because of it's potential adverse effect of blood pressure increment. We recommend that dosage reduction or treatment discontinuation should be considered instantly when serious treatment-emergent hypertension with administration of venlafaxine developed.