It is assumed that people who have higher levels of emotional intelligence are using them in more adaptable way and consequently have less inappropriate behaviours connected with emotional reactions such as aggressive or passive behaviour. The aim of this study was to examine relationship between emotional intelligence, aggressiveness and assertiveness in children attending higher grades of primary school. This study was conducted on 178 pupils; 93 boys and 85 girls from 12 to 15 years old (M=13.37). Study was conducted in paper-pencil form. Data was collected with 5 questionnaires: sociodemographic questionnaire, Emotional skills and competence questionnaire (ESCQ), Reactive–Proactive Aggression Questionnaire (RPQ), Teacher evaluation of pupils aggressiveness and Assertiveness Questionnaire. Results showed that boys have better abilities of expressing and naming emotions in comparison to girls, and that teacher rated them more aggressive than girls. In addition, older pupils have higher levels of both proactive and reactive aggression than younger pupils, but teacher evaluation of general aggression was higher for younger pupils. Higher emotional intelligence is correlated with higher assertiveness in all pupils. Girls who are more assertive are less proactively and reactively aggressive and more emotional intelligent girls are less proactively agressive. Older pupils who are assertive and have higher abilitiy to express and name emotions are less proactively agressive. Boys who are proactively agressive have higher ability to perceive and understand emotions and to express and name emotions. With set of predictor variables there was 44% explained variance of assertiveness in girls while academic success and ability to regulate emotions were significant predictors. In boys, ability to express and name emotions is significant predictor and explained variance of assertiveness is 39%. Significant predictors of assertiveness in younger pupils are academic success, ability to express and name emotions and ability to regulate emotions. Explained variance of assertiveness is 45%. In older pupils, ability to regulate emotions is significant predictor and explained variance of assertivness is 34% .