Around 90,000 Hmong in Thailand are not migrated Hmong. These Hmong is the descendants of the Hmong who has migrated from China through Lao and has been in Thailand for 100 years ago. Some is the descendants of the Hmong who has migrated from Mynmar and has been in Chiang Mai and Mae Hong Son. The Hmong rapidly adopt themselves to new economic condition and environment. The Hmong expand to the highland that is not owned. The rapid growth of population is related to the expanding of the land and it in a critical condition for the big household. The government’s policy focuses on abolishing the opium poppy cultivation, limitation of deforestation and controlling the migration, so the Hmong traditional economic system has been stucked whereas a number of the Hmong has been migrated because of the government’s security policy. The increasing controlling of the government leads to the highland roads network, so the highlander can conveniently travel to market at the lowland. The Hmong economy response to the changed condition including the cash crops cultivation with new techniques. The Hmong fertility has been increased last 5 years ago after Thai population has been decreased for 20 years. The rapid decreasing of fertility in the rural community relates to the perception of reducing chance for cultivation. It is a cause from the new land regulation whereas the Hmong population in the urban has been decreased because of high cost of raising children, decreasing of mortality, but the fertility is still high. In the meanwhile, the women prefer the modern labouring and health care and the educational level of the women is still low when the mortality is decreasing. The researchers indicate that the rapid socio-economic change among the Hmong has related to the willing to accept the new innovation with economic use. This is shown in the ready accepting the new various kinds of plants and the cultivation system and the basic social change. Recently, some Hmong women gain their own economic profit with the income of their own trading and cultivation. The economic condition has accessed the Hmong behaviour which are different from the other hilltribes in Thailand. The Hmong can adapt themselves to the changing economic condition by adapting their traditional behaviours while their ethnic identity can be maintained. (abstract)