Abstract: Aggression at schools has become an increasing concern to public health professionals. It's a multidimensional problem with biological, psychological, social, and environmental roots. Assertiveness is a kind of communication style that plays a key role in communicating successfully and effectively with others Aim: to assess aggressive behavior and assertiveness among preparatory school students. Design: A descriptive research design was used to conduct the current study. Setting: The study was conducted at Huda Sharawy preparatory school, El-Shaheed Ahmed Hamdy preparatory school for Girls, 25 January preparatory school and Mahatet El- kahraba preparatory school, Helwan, Cairo. Sample: A simple random sample of 176 students was selected from preparatory school students at 1st grade in El-Masara district during the academic year 2021-2022. Tools: Data were collected by using the following tools: Socio-demographic characteristics questionnaire, Aggression questionnaire and Assertiveness formative questionnaire Results: (62.5%) of the studied students have mild level of total aggression. While, (4%) of them have high level of total aggression. (47.2%) of the studied students are non assertive. While, (43.2%) of the studied students have average assertiveness and (9.6%) of them have high assertiveness. Conclusion: Nearly two thirds of the studied students had mild level of aggression while the minority of them had a high level of aggression. Less than half of them were non assertive and had average assertiveness. There was a statistically significant correlation between total aggression of studied students and their total assertiveness scores. Recommendations: Applying assertiveness training program to help students differentiate between assertion and aggression.