Morphine is the only opioid that has been found effective for the relief of dyspnea in cancer patients. However, efficacy has not been fully demonstrated for other opioids such as fentanyl. Here, we report a case of lung cancer in which the use of fentanyl was effective for the relief of dyspnea. The patient was an 88-year-old man who had cT4N2M0, cStage IIIB lung cancer with right bronchial involvement and mediastinal lymph node metastases. Although the patient complained of dyspnea, he was not given morphine due to underlying renal dysfunction. He instead received oxygen therapy, and treatment with oral steroids and oxycodone. As oral administration became more difficult with subsequent lung cancer progression, the patient underwent opioid switching from oxycodone to subcutaneous injections of fentanyl. Dyspnea was not exacerbated following the switching, and was thereafter effectively managed by increasing the fentanyl dose and using rescue medication. Fentanyl is suggested to be a possible therapeutic option for dyspnea in cases where the use of morphine is difficult.