This study aims to determine the effect of the habit of expressing the debate technique on student assertive behavior. This type of research is experimental research with a pre-test and post-test group design. The subjects of this study were students of class X-10 Man 2 Model Medan, amounting to 18 students who had low assertive behavior determined from the results of the pre-test questionnaire. The instrument used was a questionnaire to collect data about assertive behavior that had previously been tested to determine the validity and reliability of the questionnaire. The data analysis technique uses a different test (t-test). The results showed that there was an influence of the habit of expressing opinions on students' assertive behavior.