In rural area ofThailand, a lot of habitants cannot use Thai legal system and has had to obey pre-modern common law. On studies of Thai legal system, many researchers have found rural Thai people adaptation to modern Thai legal system. This topic has contributed for developing and improving quality of life, especially people living in North and Northeast Thailand. However, no study has been made for Hill Tribes in Northern area, because of barriers of language and long distance from city area. This research aims to describe the law consideration of the mountainous people who must choice between a Thai modern legal system and their common law system. This article aims to clarify hill tribes legal situation for contributing hill tribe people's life improving by survey in the Chiangmai prefecture interview. And this Thailand's research is to contribute maintaining the legal system of the minority in other developing districts.