Background: Recognition of the factors related to doing preventive behaviors against children tendency to addictive drug such as role of parents is necessary. This study was performed aiming to determine the role of fathers in prevention of children tendency toward addictive drugs based on theory of planned behavior. Materials and Methods: This was a descriptive cross sectional study. The research community was Yazd fathers in a sample of 180 that were selected by multistage random sampling method. Data collection tool was a questionnaire in three parts, seven demographic questions, attitude four items, subjective norms four items, perceived behavioral control two items, behavioral intention five items and nine questions of behavior completed in self-report. Data were analyzed by using SPSS-18 such as independent T-test, ANOVA, Pearson correlation coefficient and regression at α = 0.05. Results: The age range of participants was 30-59 years with the mean of 40.38±5.34. Items that achieved highest scores necessity to do behavior in attitude section, confirmed wives in subjective norms section, difficulty of doing behavior in perceived behavioral control section, beginning behavior from tomorrow in behavioral intention section and creating heartily relationship with children in behavior section to prevent children from tendency toward addictive drugs. The highest score was achieved in subjective norms structure. Attitude of fathers who were employees, homeowners and with a bachelor's degree or higher level of education, perceived behavioral control of fathers with no history of addiction in family or friends, divorced fathers' behavioral intention, and fathers' behavior with a bachelor's degree or higher level of education and with no history of substance abuse in family or friends were more positive in prevention of their children tendency to addictive drugs. Subjective norms and behavioral intention predicted 23.5% of the variance of the behavior. Conclusion: Subjective norms and behavioral intention, on which emphasis can help educational programs be more effective, were the most important factors in preventive behavior.