Outpatient rehabilitation (OR) and outpatient day long-term care (ODLC) services are frequently used by older adult patients in Japan. However, there is a need to clarify that OR service, which has more rehabilitation professionals than ODLC, has the role of providing rehabilitation. This retrospective study examined the impact of OR services by comparing the two services based on City A data from the care-needs certification survey conducted between 2015 to 2017. We performed a propensity score matched analysis to compare the changes in the care level and function of OR and ODLC users after two years. The results showed that OR users showed a lower deterioration in care levels and less decline in the activities of daily living (ADL) in dementia and adaptation to social life. In the analysis of older adults requiring support, OR users had a lower deterioration in care levels and less decline in the ADL in dementia and behavioral and psychological symptoms than ODLC users did. There was no difference between the two services with respect to older adults requiring long-term care. The OR service has had an increasingly preventive effect on the deterioration of care levels compared to the ODLC service, which was particularly evident in older adults requiring support.