Introduction: Child abuse is a deliberate act of violence against children under the age of 18 years. One of its major complications is the aggression of children and, as a result, an increase in crime in society and a reduction in the success and quality of life in children. The aim of this study was to determine the relationship between child abuse and aggression in primary school students in Sanandaj City-Iran. Methods: In this cross sectional study, the population included 381 primary school students (10-12 years old) living in Sanandaj. Samples were selected through multistage cluster sampling. Eysenck Aggression Questionnaire and the Majdzadeh Child Abuse Questionnaire were used. Data were analyzed using SPSS-18 software with Chi-square test for statistical analysis. Results: Of the 381 students, 171 (44.9%) were male and 210 (55.1%) were female. Chi-square test showed that there was a significant difference between aggression with gender (P=0.01) and grade (P=0.036). There was also a significant relationship between child abuse and father's education (P<0.05). There was a significant relationship between aggression and different types of child abuse (psychological, emotional, physical and neglect) (P<0.05). Conclusion: Considering the increasing prevalence of child abuse and its direct relationship with aggression in children, proper planning to reduce this social problem, it seems necessary to conduct educational classes for parents and teach them the proper way of communication with children.