Objective: This study objected to investigate temporal changes in opioid usage one week before death in terminally ill pediatric cancer patients, objecting to identify factors influencing opioid use. Methods: We retrospectively reviewed charts of pediatric cancer patients who died at the National Cancer Center Hospital between January 1, 2014, and October 31, 2022. Opioid morphine equivalent daily doses per body weight (OMEDD/kg)(mg/kg/day) were analyzed for age groups (<14 years vs. ≥14 years) and tumor types (hematologic malignancies vs. solid tumors) one week, three days, and one day before death. Results: A total of 36 patients were included in this study. Patients aged <14 years had higher OMEDD/kg compared to those aged ≥14 years at all three time points. Hematologic malignancy patients had lower OMEDD/kg compared to solid tumor patients one week and three days before death, with a trend towards equivalence on the one day before death. Conclusion: The study suggests that opioid use in terminally ill pediatric cancer patients varies according to age and tumor type, highlighting the need for individualized consideration of patient factors.