Intergroup anxiety can undermine positive intergroup relations. This Registered Report presents two preregistered online studies testing a mental contrasting intervention to reduce intergroup anxiety towards Black individuals. Previous work aimed to inoculate anxiety by having participants imagine a threatening intergroup experience followed by a positive one, compared to only imagining positive interactions. In Study 1 (N = 300), White US adults were randomly assigned in a 2 × 2 design to imagine either a negative-then-positive interaction (intervention) or positive-only interactions with an outgroup (Black) or ingroup (White) member. State anxiety was measured immediately before and after the second imagined interaction, followed by prejudice and contact intentions. Study 2 (N = 149) replicated the outgroup conditions and tested whether imagining a neutral-then-positive interaction reduced anxiety relative to imagining positive-only interactions. Contrary to preregistered predictions, Study 1 showed higher intergroup anxiety in the intervention condition and a significant condition × time interaction. These effects did not replicate in Study 2. Across both studies, the intervention did not significantly reduce prejudice or increase contact intentions. Overall, the preregistered tests did not support the hypothesis that this intervention reduces intergroup anxiety or related outcomes, constraining claims regarding its robustness and generalizability.