The purposes of this research were: 1) to study the origin and development process of the Black Dragon Gang (hereinafter refers to as “the Gang”, 2) to study the transformation process of the Gang’s action which finally perform the leading role for the development of Khon Kaen City, and 3) to obtain the lessons learned from the study case of the Gang which would lead to the guideline for the development of the vulnerable youth. The sample group selected by the purposive sampling were : 10 members of the Gang, 8 community leaders and the public authorities concerning the mental and behavioral adjustment for the Gang’s members, the Gang members’ relatives and neighbors who were either directly or indirectly treated by the Gang’s actions. The results revealed the foundation of the Gang of 500 uneducated youth members which was dated back on 1998 under the leading role of Mr. Pradith Asucheeva (Piak). Not only to be accepted and respected by another one, the sacred symbol used as the Gang’s emblem had significantly attracted the youth who were being neglected by their uninterested parents and had gradually increased the Gang’s member from 14 to 500 nationwide. There were 3 tiers regarding the structure of the Gang : the Head ( Black Dragon) , the Vice Head (Tiger- Dragon), and the common members (Dragon). For more than 10 years, the Gangs’ illegal and anti - social norms actions had been causing social problems in many aspects . That was the results of the Gang’s efforts for the youth members’ values shaping considering their fundamental needs for self-esteem, self – proudness, and the success of life. However, the actions of the group with collective values and psychological forces that treated their families, neighbors, and societies, had been investigating and deterring by the police officers and the public authorities. The lesson learned from the study case of the Black Dragon Gang, which could lead to the protection and development of the vulnerable youth, was the significant role of the Gang’s head as a driving force for either positive or negative actions of the Gang’s member. Therefore, the family’s inspiration for the adjustment of the Gang’s head behavior from the illegal actions to the legally professions was also considered as the prompt adjustment for the member’s. Thus, the family’s attention, the community’s leader and community members’ understanding and acceptance, were accepted as the guideline for the behavioral adjustment of these youth. For instance, Khon Kaen Municipality’s supportive roles in persuasion of the uneducated and vulnerable youth to return to the respective educational system, the roles of the concerned agencies such as the Office of Vocational Education for the vocational promotion , as well as the Quality Learning Foundation for the supportive actions for any current activities organized by related agencies. The collaborative actions of concerned parties such as the Head of the Gang, families, communities, local governments organizations, educational institutions, and the youth development agencies, had effectively created the concrete efforts for the behavioral adjustment of the members of the Black Dragon Gang ,as well as the efforts for the protection and development of the vulnerable marginal youth, which is one among the important factors for the peaceful society.