Purpose: This study was done to examine factors affecting cancer preventive behavior in middle-aged people. Method: The research design for this study was a descriptive survey design using convenience sampling. Data collection was done using self-questionnaire with 203 middle-aged people in Seoul and G city. Data were analyzed using t-test, ANOVA, Pearson correlation coefficients and stepwise multiple regression with the SPSS Win 20.0 Program. Results: The mean score of cancer preventive behavior was $3.43{pm}.14$ out of 5. Cancer preventive behavior showed a significantly positive correlation with knowledge about cancer (r=.24, p<.001). In the multiple regression analysis, gender, perceived health status and knowledge about cancer were significant predictors and explained 14.5% of cancer preventive behaviors. Conclusion: Findings of this study allow a comprehensive understanding of cancer preventive behavior and related factors by middle-aged people. However, further study with a larger random sample from various living environment is necessary.