Older adults are becoming increasingly interested in and developing the ability to use mobile fitness (mFit) technology to stay healthy, independent, and socially connected. However, relatively little attention has been paid to older adults' mFit technology use and related health outcomes. Drawing on the mFit technology feature set model and the theory of social support for health, this study develops a model that explores how older adults' mFit technology use influences their physical and psychological well-being. The proposed model was tested using survey data collected from 189 older adult users of mFit technology. The results showed that the use of mFit technology was positively associated with older adults' physical and psychological well-being. At the feature set level, the study also established that three mFit technology feature sets played different roles in enhancing physical and psychological well-being. Notably, the findings suggest that the promotion of older adults' mFit technology use should not be left to individual discretion. Instead, older adults' use of such technologies should be supported and promoted at the community level. The findings of this study provide insights for researchers and practitioners who seek to promote older adults' health via mFit technology. For academia, this work conceptualizes the social support aspect of mFit technology use and reveals its role in shaping the effects of older adults' mFit technology use on their health outcomes. In practice, this research provides useful insights into design strategies that could help optimize older adults’ use of mFit technology for improving their physical and psychological well-being.