Accessibility to services and amenities is related to social participation in older adults. However, the mechanisms underlying this association are not clear. Transit use and walking may be potential mediating variables. The aim of this study was to investigate whether frequency of transit use and frequency of walking mediated the relationship between accessibility to services and amenities conducive to social participation (SACSP) and social participation itself among a sample of older adults. Participants were 519 older adults from the VoisiNuAge study. Multiple mediation and separate mediation analyses were conducted to investigate whether frequency of transit use and frequency of walking mediated the association between accessibility to SACSP and social participation, controlling for sociodemographic variables. Results showed that transit use was a significant mediator in multiple and separate mediation analyses. Walking frequency was not a significant mediator in multiple mediation analyses, and conflicting results were observed for separate mediation analyses involving walking. We conclude that the association between accessibility to SACSP and social participation seems to be partly mediated by transit use, but results involving walking should be interpreted cautiously.