This article is about economic systems and ethnic relations in northern Thailand. Because of their distinctive ecological areas and products in each group, they have to depend on other groups products with different ecology. Therefore, there is widely economic exchange between the group, especially the trading dependence between the highlanders and the lowlanders. However, there is less social relation, so the ethnic groups can maintain their different way of life and cultural freedom. They depend on exchanging through middlemen such as hagglers, caravans and stores rather than directly trading with the marketing centers. When opium, a main cash crop of the highlanders, is noticed as illegal and the land is limited, there is a conflict between the lowlanders and the highlanders and Thai government tries to assimilate the culture with many methods.