The purpose of this research was to study the effectiveness of health education program through group problem solving on opisthorchiasis preventive behavior among the poeple in Amphoe Tha U Then Narkornphanom. The samples were housewives of which their family members were infected which Opisthorchis viverrini. The samples were devided into experimental group and comparison group. The experimental group, consisted of 97 housewives received health education program through group problem solving. The comparison group consisted of 43 housewives received no additional health education activities. The data were collected by interview questionnaire, observation check list developed by researcher. Katos thick smear technique were employed to find opisthorchis eggs in stool both at before and after the experiment. The statistical methods used for data analysis were : percentage distribution, mean, standard devitation, Students t-test, Paired Samples t-test and Z-test Level of significance was set at 0.05. The main results were as follows: 1. After the experiment, the mean score regarding to the knowledge and believes about opisthorchiasis of the experimental group was significantly higher than before the experiment and higher than that of the comparison group (P-value < 0.001) 2. After the experiment, the mean score regarding to the intention and practice about preventing opisthorchiasis of the experimental group was significantly higher than before the experiment and higher than that of the comparison group. (P-value 0.001). 3. After the experiment, family members in the experimental group indicated that they eat raw fresh water fishes less frequent than the comparison group (p-value <0.001) 4. After the experiment, Prevalence rates of Opisthorchis viverrini infection among family members in the experimental group was significantly lower than in the comparison group (p-value <0.001) 5. After the experiment, Incidence rates of Opisthorchis viverrini infection among family members in the experimental group was significantly lower than in the comparison group (p-value<0.001) 6. After the experiment, Reinfection rate of Opisthorchis viverrini infection among family members in the experimental group was lower than in the comparison group (p-value = 0.01) The research findings shown the effectiveness of group problem solving method in effecting changes in knowledge, believes, intention and practices in preventing opisthorchiasis. Thus, group problem solving method may be replicated to a larger population.