Background: The aim of this study was to clarify the decadal trends in the structure and usage status of palliative care units in Japan and the association with length of stay. Methods: We conducted a secondary analysis of data from nationwide surveys of palliative care units conducted by Hospice Palliative Care Japan from 2002 to 2012. Length of stay was divided into three categories (within 30 days, 31 to 60 days, and 61 days or more). Results: Significant decadal trends in usage status were observed: the mean annual number of admitted patients (119±55 persons in 2001, 163.0±77.7 in 2011, p＜0.001), and deaths (99±44, 136±58, p＜0.001) increased and the mean length of stay in a palliative care unit (8±15 days, 39±15, p＜0.001) decreased. Palliative care units with a shorter mean length of stay had significantly more admitted patients, and more discharged patients, and a significantly lower mean ratio of death to discharge, and a lower bed availability rate. In contrast, length of stay was not significantly associated with the structure of palliative care units, including the type of units, number of inpatient beds, percentage of private rooms, and number of staff. Conclusion: The features of decadal trends in the structure and usage status of palliative care units in Japan were a shortening of length of stay, and an increase in the number of patients. Palliative care units with a shorter mean length of stay cared for a larger number of terminally ill patients.