Objectives: The purpose of this study was to examine the relationships between hypertension knowledge, attitude, and preventive activities of 20-30 years prehypertension adults. Methods: The subjects for this study were 178 prehypertension adults in J city. The data were collected using the questionnaires for knowledge, attitude and preventive activities. The data analysis was done by descriptive statistics, independent t-test and multiple regression analysis. Results: The mean of hypertension knowledge was 10.99 out of 18, attitude was 4.28 out of 5, and prevention activities was 5.32 out of 7. The influencing factors for hypertension preventive activities were attitude, perceived health status, marrital status and gender which accounted for 82.6% of the total variance. Conclusions: Hypertension attitude was identified as a variable that affects hypertension preventive activities. For preventing hypertension, national campaign and health education program in each prehypertension early adults need to be built.