This paper analyzes whether the current adult guardianship in Taiwan promotes “positive aging” through relevant psychosocial theories. First, the model of “successful aging” emphasizes the connection between individual and society. However, a person under guardianship not only loses legal capacity so that he/she is not able to perform any transactions in the market, but will also be deprived the right to vote, meaning that social participation becomes impossible. Second, the theory of “selection, optimization with compensation” points out that seniors select and optimize their best abilities and most intact functions while compensating for declines and losses. Therefore, every senior may have different selection and strategy of optimal aging. Under adult guardianship, there is no way for the ward to make any selection because of legal incapacity. At the same time, the guardian, that is, the plenary legal representative has the authority to make all decisions for the ward under the “best interest rule”, which does not require the guardian to follow the preference of the ward. Since the “selection” of SOC model does not exist in guardianship, it is impossible for the ward to continue to pursue optimal goals and compensate anything. As a result, the adult guardianship in Taiwan hinders people from successful or optimal aging and should be improved as soon as possible.