Objectives: The purpose of this study was to examine the effect of knowledge on dementia and internal health locus of control on dementia preventive behaviors among older people living alone. Methods: The subjects were 158 older people living alone over 65 years. Data collected from January 14 through February 13, 2015. Collected data were analyzed with Independent t-test, One-way ANOVA and multiple regression analysis. Results: Dementia preventive behavior based on general characteristics showed statistically significant difference in level of education, perceived level of health, and acquisition information on dementia. The factors affecting dementia preventive behaviors were as follows: high school grades and over, ``average`` perceived level of health, ``good`` perceived level of health, acquisition of information on dementia, knowledge on dementia, and internal health locus of control. The explanatory power of these factors was 28%. Conclusions: The findings suggest that in order to promote dementia preventive behaviors of the older people living alone, it is necessary to encourage this population, particularly those with low educational levels, poor perceived health and with no information on dementia, to participate in programs on dementia prevention.