We describe six patients with terminal cancer whose delirium improved after they started quetiapine (QTP). Haloperidol (HPD) had failed to improve their delirium, and they had suffered adverse effects, including over-sedation, extrapyramidal signs and dysphagia. We prescribed QTP to improve their delirium. We evaluated the severity of the delirium using the Japanese version of the Memorial Delirium Assessment Scale (jMDAS) before QTP treatment and 3, 7 and 14 days after QTP administration. The basal the Japanese version of the Memorial Delirium Assessment Scale score ranged from 18 to 24. Effective doses of QTP in the present cases were 12.5–50 mg/day. Delirium improved in all patients, and no significant adverse effects were observed. Several factors appear to contribute to symptoms of delirium in patients with terminal cancer. These causative factors are usually complicated and delirium often is refractory to usual pharmacotherapy, involving typical neuroleptics like HPD. QTP, however, appeared to be useful for delirium treatment in patients with advanced cancer.