The César Award for Best Actress in a Supporting Role (French: César de la meilleure actrice dans un second rôle) is one of the César Awards, presented annually by the Académie des Arts et Techniques du Cinéma to recognize the outstanding performance in a supporting role of an actress who has worked within the French film industry during the year preceding the ceremony. Nominees and winner are selected via a run-off voting by all the members of the Académie.