We investigated the usefulness of suvorexant for complicated delirium in patients with cancer who experience sleep disturbance during hospitalization. Nine patients with malignant tumors complicated with symptoms of delirium and insomnia were included in this study; their palliative care was managed by the palliative care team of our hospital for a period of one year from April 2016 to March 2017. A retrospective follow-up study was then conducted. The Japanese version of DRS-R98 was used to evaluate the severity of the patient's delirium. The total severity score of DRS-R98 significantly decreased after the administration of suvorexant when compared to the score before its administration(6.66±1.73 vs 10±3.20, p=0.0031). In addition, suvorexant did not exhibit any harmful effects. Our results indicate that suvorexant was useful in alleviating delirium symptoms in cancer patients who experience sleep disturbance.