We encountered a case where opioids were effective for excessive sweating caused by secondary generalized hyperhidrosis associated with cancer. ​​A 64-year-old woman diagnosed with metastatic renal cell carcinoma was admitted to the palliative care unit with right hip pain caused by bone metastasis and sudden excessive sweating. An increased dose of fentanyl transdermal patch provided pain relief. Excessive sweating seemed to have occurred due to neoplastic fever initially, but antipyretic analgesics and steroids were ineffective. Prophylactic use of immediate-release oxycodone provided excessive sweating relief. Finally, we consider that hypothalamus and fentanyl transdermal patch were involved in excessive sweating. Opioids may suppress sweating by acting on the hypothalamus.