This study aimed to identify the self-assertion and its relationship to aggressive behavior among the students in post basic education. Based on the variables which Muscat schools face.the study sample consisted of 440 students who were selected randomly from beyond primary grades XI and XII in Muscat governate schools during the academic year (2011-2012). To achieve the objectives of this study the researcher used a descriptive linking approach that tries to describe linking approach that tries to describe and analyze self assertiveness and its relationship to aggressive behavior among students. Also to answer the study questions several tests were found suitable to show the results such as Cranach Alpha to ensure the stability of the study standards, "T-Test to know the significance of the patterns (dimensions) of aggressive behavior and self assertiveness of students, also ANOVA analyze which shows the significance of sexual variance in aggressive behavior and to identify the coefficients correlation between dimensions (patterns) of aggressive behavior and self-association. The study results showed that overall level of aggressive behavior by responding subjects that they were intermediate in general with respect to physical aggression, but it was fairly high with regards to some dimensions of aggressive behavior such as verbal aggression, and all averages of aggressive behavior dimensions were located in middle range, physical aggression had reached the maximum levels by 3.16 average and standard deviation of 1.03, verbal aggression comes next by 3.1 average and 1.05 standard deviation in which emphasize on the use of aggression and hostilities by 2.97 and anger characterized by students after the primary education shows that they have a high self-assertiveness in their personalities. The result of this study shows the existence of a relationship between aggressive behavior and self-assertiveness in students by correlation coefficient of (0.20) which is statistically significant at the level of (0.01).