This study examined the effect of power imbalance and the presence of third parties on vengeful reactions to harm. At the onset of their interaction, participants were unjustly harmed by a confederate who had either more or less power than they had. As predicted, in the presence of a justice-concerned third party, upward revenge (people of low power taking revenge against those of high power) was greater than downward revenge (people of high power taking revenge against those of low power). However, in the absence of a third party, downward revenge was greater than upward revenge. These findings highlight the important role of third parties in determining vengeful behavior in situations of power imbalance and add additional evidence for the importance of justice concerns in revenge.