The positive role of secure attachment in reducing intergroup biases has been suggested in prior studies. We extend this work by testing the effects of secure attachment primes on negative emotions and aggressive behaviors toward outgroup members across four experiments. Results from Studies 1A and 1B reveal that secure attachment prime, relative to neutral, can reduce negative outgroup emotions. In addition, Studies 1B and 3 results rule out positive mood increase as an alternative explanation for the observed effects. Results from Studies 2 and 3 reveal that secure attachment primes can reduce aggressive behavior toward an outgroup member. The effect of secure attachment primes on outgroup harm was found to be fully mediated by negative emotions in Studies 2 and 3. An interaction between secure attachment primes and ingroup identification in Study 2 indicated that the positive effects of secure attachment in reducing outgroup harm may be especially beneficial for highly identified ingroup members.