High school students who are in the development age or in the last class and have chance to win the university exams or disposal stage of the business life must also have a high level of assertiveness. In this context, the purpose of this research is to compare the assertiveness levels of high school seniors. The study group consists of 312 high school seniors studying at five different high schools in Manisa center. In this research, to measure the level of assertiveness, the Rathus Assertiveness Inventory, which was developed by Rathus (1973) and translated into Turkish in 1980 by Voltan, was used. The demographic information of the participants was obtained by using "Personal Information Form". The evaluation of the datum which was gained from the test subjects in this research was done by using T-Test, one-way analysis of variance and Tukey Test. At the end of this research, statistically meaningful differences were found out in the students' scores of assertiveness according to their respective schools. When demographic information of the students were evaluated, statistically meaningful differences in the scores of assertiveness were found with regard to education level of their parents. Statistically meaningful differences in the scores of assertiveness were not found in relation to the gender of the students, their engagement with sports and the occupation of their parents.