Background: Adults with intellectual disabilities often experience mobility limitations. Baduanjin, a mindfulness-based exercise intervention, can exert positive effects on functional mobility and balance. This study examined the impact of Baduanjin on physical functioning and balance of adults with intellectual disabilities. Method: Twenty-nine adults with intellectual disabilities participated in the study. Eighteen received a Baduanjin intervention for 9-months; 11 participants did not receive any intervention (comparison group). Physical functioning and balance were assessed using the short physical performance battery (SPPB) and stabilometry. Results: Participants in the Baduanjin group experienced significant changes in the SPPB walking test (p = 0.042), chair stand test (p = 0.015), and SPPB summary score (p = 0.010). No significant changes between groups were observed in any of the variables assessed at the end of the intervention. Conclusions: Baduanjin practice may cause significant, albeit small, improvements in physical functioning of adults with intellectual disabilities.