Teeth brushing is a way to get a healthy mouth. For some people with intellectual disability, teeth brushing is a difficult thing to do because of their limitation. This paper focus on a 15 years-old with intellectual disability who has difficulties in doing teeth brushing. Behavior therapy is a frame of reference used to assess, to evaluate, and to change a behavior aims to know effectiveness of behavior therapy in teeth brushing. The data was collected using occupational therapy’s instrument form. The author suggest behavior therapy will be effective in teeth brushing.