Nightmares are common in patients with advanced cancer. However, there are no standard treatment of nightmare in patients with cancer. We experienced a case with nightmares improved by Saikokaryukotsuboreito (SRBT). An 82-year-old man with malignant lymphoma experienced insomnia and nightmares. Antidepressants, orexin receptor antagonists, and atypical antipsychotics failed to improve the symptoms, but SRBT immediately eliminated his insomnia and nightmares. SRBT, an herbal medicine, has been used in a variety of clinical situations for treatment of stress-induced psychiatric symptoms, i.e., anxiety, depression, and insomnia, without serious adverse events. Several reports suggest that SRBT improves depression and anxiety with the effects on chronic stress-induced disruption of hypothalamo-pituitary-adrenal axis. The effects of SRBT might have improved nightmares in this case. SRBT may be a drug of choice in the treatment of nightmares in patients with cancer.