Objectives A growing body of literature indicates that social engagements, such as intergenerational programs, are effective strategies to improve a range of cognitive abilities. The present study examined whether the intergenerational program—REPRINTS—prevents age‐related hippocampal atrophy. Methods After comprehensive baseline assessment, participants were allowed to decide whether to participate in the REPRINTS intervention or in the control group, which required only completion of assessments. REPRINTS participants engaged in group activities that involved reading picture books to children at kindergarten and elementary schools, once every 1 to 2 weeks. A follow‐up assessment was conducted after 6 years. Two MRI scans were performed, one immediately after baseline assessment and the other after 6 years. Volumes of the hippocampus, thalamus, and caudate nucleus were derived from automated segmentation. The analysis included 17 REPRINTS and 42 control‐group participants. Results There was no significant difference in any variable of participants' characteristics at baseline between the REPRINTS and control groups. Hippocampal volume significantly declined in the control group but was maintained in the REPRINTS group. No significant differences between groups in thalamus or caudate nucleus volume were observed. Although cognitive function was unaffected by the program, greater decreases in hippocampal volume were significantly correlated with greater decreases in cognitive performance scores. Conclusions Our results suggest that the REPRINTS intergenerational program has protective effects on age‐related hippocampal atrophy in older adults. These changes precede improvements in cognitive performance, suggesting the validity of the concept of brain plasticity in later life following social engagement.