The present invention relates to a bispecific antibody binding specifically to a-synuclein and IGF1R and a use of the bispecific antibody in preventing, treating, and/or diagnosing a-synucleinopathies, which are diseases related to a-synuclein or an aggregate thereof. In the present invention, an a-syn antibody or an antigen binding fragment thereof is allowed to pass the blood-brain barrier and to exert the function thereof in the brain, and the half-life is prolonged so that the medicinal efficacy can be maintained for a long period of time.
