The present study examined preschoolers' cognitions about justice of punitive aggression. In Study 1, 3- and 4-years-olds were presented with picture stories depicting either the character's punitive aggressive behavior or assertive behavior for correcting other's transgression. Following each story, participants were asked; (1) to judge whether each behavior was effective in correcting transgression or not; (2) to rate each behavior in terms of relative goodness. The results indicated that 3-years-olds justified punitive aggressive behavior to some degree regardless of effectiveness, while 4-years-olds justified punitive aggressive behavior only when it seemed effective. In Study 2, 4-years-olds discussed about justice of punitive aggression. The results indicated that participants who believe punitive aggression being effective justified it consistently, while most participants argued that justice of punitive aggression changed with situations. Preschoolers' cognitions about justice of punitive aggressive behavior would be strongly influenced by beliefs about effectiveness of punitive aggression.