This qualitative research within the project entitled "Multiprofessional Intervention and training for Ongoing Volunteer-based Community Health Programs in the Northeast of Thailand (MITV-NET) " was aimed at explaining changes of health behavior of community people in the Northeast after the intervention. The participants comprised 15 community volunteers and 27 villagers. Data were collected by indepth interview, focus group discussion, participation and non-participation observation, and note taking. Analyses were conducted in parallel with data collection, through content and comparative analysis. It was found that the health behavior fell into 2 categories: easy-to-change and difficult-to-change. The former involved fun activities joined by community people that improved their health or made them recover from illnesses after a short period without becoming addicted. These activities could be done by themselves, for example, exercising and cooking. The difficult-to- change health behavior is habitual, for example, chewing betel nuts or eating uncooked food. The following factors were found affecting behavioral changes: 1) underlying disease; 2) enjoyment in doing activities; 3) habitual behaviour; 4) improved health in a short period; 5) ability of community leaders and volunteers; and 6) community health-supporting resources. It is suggested that improving people's health requires cooperation of community people through fun activities and some initial external support. People who persist in bad habits should be encouraged to stop by showing them health deteriorating effects.