The thesis examined the personal characteristics, socio-economic factors, factors affected by and problems in adopting opium replacement crops of Hmong farmers at Nong Hoi Kao Village. The data were collected from 118 household heads. It was found that the average age of the sample group was 40.06 years, with 52.5% being uneducated and illiterate in Thai. Most had experienced the crop replacement procedure for over five years with an average annual household income of 64,168 baht and average land ownership of 3.2 rai. Contacts were made and information was obtained mostly through officers of the Royal Development Project. Each household had on average 3.62 persons in household labor, 45.8% never attended agricultural training, few were satisfied with the prices of opium replacement crops due to price fluctuation, and most did not hold any leadership positions in the village. The factors related to the adoption included age, level of Thai proficiency, satisfaction with prices of replacement crops, agricultural training experience, and contacts with the officers. The problems related to crop replacement included high production cost, marketing problems, lack of capital, insufficient labor, and insufficient water for cultivation in the dry seasons.