Aging is associated with decreased self-initiated use of effective elaborative encoding strategies. Little is currently known regarding what factors drive age differences in self-initiated encoding strategies. The present research investigated whether age differences in prefrontal gray matter integrity contribute to age differences in self-initiated elaborative encoding strategies. The relationships between age, prefrontal regional gray matter volumes, and overall use of self-initiated elaborative encoding strategies were examined in healthy younger and older adults. Gray matter volume was calculated from structural MRI scans using Freesurfer. Encoding strategy use was assessed by retrospective item-by-item strategy self-reports given after a verbal intentional encoding task. Left caudal middle frontal gray matter volume mediated the effect of age on overall self-initiated use of elaborative encoding strategies. This suggests that age-associated declines in prefrontal gray matter integrity significantly contribute to age-associated declines in effective encoding strategies.