This study was aimed at investigating the effectiveness of assisted therapy (ACT) on manual dexterity in older adults with Down syndrome (DS). Nine older participants with DS, aged 31-52 years old, completed a 30-min stationary cycling session, three times per week for eight weeks of ACT intervention, pedaling at 35% higher than voluntary speed. Another eight older participants with DS, aged 30-51 years old, participated in the voluntary cycling (VC) intervention, pedaling at voluntary speed, as the comparison group. Manual dexterity measured by the Purdue Pegboard Test, and outcome expectations measured by the Exercise Perception Scale, were tested before and after the interventions. After both exercise interventions, the results showed that the non-dominant hand and bimanual subtests of the Purdue Pegboard were significantly improved. The outcome expectations were elevated at marginally statistical level as well. It is speculated that continuous cycling exercise, VC and ACT, may stimulate peripheral sensory input to the motor areas that led to the improvements in manual dexterity and exercise perception. Even though the exact mechanisms are still unknown, the implication of our results showed that VC and ACT can improve manual dexterity in aging DS population.