Negotiating a synergized solution is challenging under optimal circumstances. Add in the challenge of cross-cultural differences, cultural collision occurs leading to worse negotiation outcomes in intercultural negotiation than intracultural ones (e.g., Adair et al., 2001; Adair et al., 2007). Given that intercultural negotiations are both challenging and prevalent, this study investigates how to improve intercultural negotiation effectiveness, and demonstrates when intercultural negotiators can in fact achieve significantly better outcomes than intracultural negotiators (i.e. cultural synergy). Drawing insights from research on cultural essentialism and its influence on intergroup relations and conflicts, I examine the interaction between essentialist beliefs and the cultural context in negotiation. Using an actor-partner interdependence model, I reveal that whether cultures collide or synergize in intercultural negotiation depends on negotiators’ endorsement of cultural essentialist beliefs. Intercultural negotiators who believed that cultural characteristics are malleable (i.e. non-essentialist beliefs) achieved higher individual gains and joint gains, compared to not only intercultural negotiators who endorsed stronger essentialist beliefs, but also intracultural negotiators. Beyond identifying why cultures collide in negotiation, these findings pave the way for future research to examine factors that help negotiators harvest cultural synergy for favorable negotiation outcomes.