Purpose: This study was to examine the relationships between knowledge about osteoporosis and cognitive factors in middle-aged women. Method: The subjects were 293 middle-aged women. Data collection was performed by using a questionnaire that included an Osteoporosis Knowledge Test, Osteoporosis Self-Efficacy Scale and Osteoporosis Health Belief Scale developed by Kim, Horan & Gendler(1991). Data was analyzed using the SPSS Win 10.0 program for descriptive statistics, and the Pearson correlation coefficient. Result: The mean osteoporosis knowledge was 14.0. The subscale means of osteoporosis health belief variables were: susceptibility 15.9, seriousness 17.2, benefits of exercise 22.9, benefits of calcium 21.4, barriers to exercise 20.9, barriers to calcium 22.5, and health motivation 18.6. The mean osteoporosis self-efficacy was 39.3 with a moderate score. There were significantly positive correlations among knowledge about osteoporosis, health belief, and self-efficacy about osteoporosis. Conclusion: Osteoporosis knowledge, health belief, and osteoporosis self-efficacy are related. Therefore, knowledge through education is an important factor in behavioral changes and it contributes to increase the health belief and self-efficacy of osteoporosis.