Aggressive and prosocial children's emotion attributions and moral reasoning were investigated. Participants were 235 kindergarten children (M=6.2 years) and 136 elementary-school children (M=7.6 years) who were selected as aggressive or prosocial based on (kindergarten) teacher ratings. The children were asked to evaluate hypothetical rule violations, attribute emotions they would feel in the role of the victimizer, and justify their responses. Compared with younger prosocial children, younger aggressive children attributed fewer negative emotions and were more likely to provide sanction-oriented justifications when evaluating rule violations negatively. Furthermore, age-, gender- and context-effects in moral development occurred. The context-effects included both effects of transgression type (i.e., prosocial morality vs. fairness) on emotion attributions and moral reasoning and the effects of the context of moral evaluation and emotion attribution on moral reasoning. Findings are discussed in terms of the role of emotion attributions and moral reasoning as antecedents of children's aggressive and prosocial behavior.