The content of this investigation focused on the spread of AIDS in Thin and Khamu communities in Nan Province. It also examined the ethnic cultural aspects that defined sexual behavior of the ethnic groups, which are traditionally strict on sexual matters and do not accept premarital sexual relationship. Additionally, this work also examined preventive and problem-solving measures on sexual behavior occurring in the communities. For instance, widows were assisted because they were once married. The assistance was meant to prevent widows from having sexual relationships with young single men, which might cause problems in their communities. Furthermore, ethnic customs and traditions also played a major role in preventing wrongful sexual behavior that might bring about the spread of AIDS in their communities.