Purpose: This correlational study was to examine the relationships between dementia knowledge, attitude, self-efficacy and preventive behavior of low income middled-aged women. Methods: The subjects for this study were 125 low income middle aged women living in I city. The data were collected using the questionnaires for dementia knowledge, attitude, self-efficacy and preventive behavior. The data analysis was done by descriptive statistics, t-test, ANOVA, Pearson product moment correlation and stepwise multiple regression analysis. Results: The mean of dementia knowledge was 13.96 out of 20, attitude was 43.98 out of 60, self-efficacy was 54.07 out of 75 and preventive behavior was 25.98 out of 36. The positive correlations were revealed between dementia knowledge (r=.458, p=.000), attitude (r=.498, p=.000), self-efficacy (r=.573, p=.000) and preventive behavior. The influencing factors for dementia preventive behavior were self-efficacy, belief in Buddhism and attitude which accounted for 42.5% of the total variance. Conclusion: Dementia knowledge, attitude and self-efficacy were identified as variables that correlate dementia preventive behavior. Also, self-efficacy is the most influential factor affecting dementia preventive behavior. On the basis of these results, it is necessary for nurses to consider using dementia knowledge and mode of efficacy expectation in order to improve dementia preventive behavior.