Scribbling is an artistic activity that is often carried out in the art therapy sessions for individual clients, partners, families or groups. Its objects are either children or adults; and it is either initiated by the clients or led by the therapists. Starting from the cognitive developmental stage theory of Piaget, the children drawing developmental stage theory (Lu Yaching, 2005) developed by this author on the basis of the children drawing developmental theory of Lowenfeld (Lowenfeld & Brittain, 1987), the analytical viewpoints of Freud's mental motive force school, and the theory of expressive therapies continum (ETC) of Lusebrink, (Lusebrink, 1990, 1991), this essay studies how the seemingly meaningless scribbling in art therapy is transformed into valuable and effective therapeutic activities. It also introduces the circumstances of scribbling in the therapeutic process, as well as a few often used scribbling techniques. Finally, it gives a few examples of client-initiated and therapistled scribbling to illustrate their transformation in the art therapy process.