Anxiety among children is one of the most common psychological disorders and it can be a predictor of many negative consequences which is why it is important to look into the predictors of anxiety. COVID-19 pandemic caused a rise in stress which also affects anxiety. The goal of this research was to examine the role of emotion regulation and intolerance of uncertainty in explaining the severity of anxiety symptoms in older primary school children. The data was collected as part of the project Determinants of emotional adjustment during normative life transitions. Data collection took place during March and April of 2021. There were 234 participants from Nikola Tesla elementary school. The age range was from 10 to 15 years old. They were questioned using Revised Child Anxiety and Depression Scale, Intolerance of Uncertainty Scale for children– short form, Cognitive Emotion Regulation Questionnaire and Stress scale. A gender differences was found in anxiety and added that there were gender differences in stress and the use of maladaptive strategies of emotion regulation. Girls reported more anxiety symptoms, more stress caused by COVID-19 pandemic and they reported more frequent use of maladaptive emotion regulation strategies than boys. A positive correlation was found between anxiety and intolerance of uncertainty, stress and the use of maladaptive emotion regulation strategies. Furthermore, intolerance of uncertainty had a positive correlation with stress, maladaptive and adaptive strategies of emotion regulation. A positive correlation was found between maladaptive emotion regulation strategies and stress. Regression analysis established the existence of partial mediation effects of maladaptive strategies of emotional regulation and intolerance of uncertainty in the relationship between stress and anxiety. The existence of mediation effects indicates the possibility of influencing anxiety by influencing strategies of emotional regulation and intolerance of uncertainty through prevention and assistance programs for primary school children.