This article discusses aggressive behavior which has been a problem that affects interpersonal and intrapersonal relations at SLB (schools for students with special needs) Negeri Rokan Hulu. This study aims to identify the forms of aggressive behavior, the causes and the strategy of handling aggressive behavior by mentally disabled children in a mild category. The research approach used in this research is quantitative using a case study type. The selection of data sources was from teachers teaching mentally disabled adolescents of a mild category at SLB Negeri Rokan Hulu who have a tendency for aggressive behavior. The method used to collect data were observation, interviews and documentation. The method used to analyze data were data reduction, data display and conclusion drawing. The results show that: (1) The factors that cause students to behave aggressively are the lack of attention and affection from the closest people so that they behave aggressively to other friends who are considered weak in order to get attention from others especially teachers at school. (2) The forms of aggressive behavior were shown verbally and non-verbally. The most frequently shown behaviors are shouting, disturbing other students who are considered weak and disobeying the rules at school. (3) There are some efforts done by the school in handing the aggressive behavior of the children. Firstly, it is important to understand and accept them and implement an active, creative, effective and fun learning process. Secondly, providing utilities needed by them in their learning process such as books, pens, pencils, and others in order to control their behaviors who do not want to learn since they argue that their books are left home. Thirdly, the mentally disabled adolescents are involved in more active communication and school activity.