Global advocates have argued in favor of increasing connectedness to nature, the benefits of which have been substantially supported for both the environment and humans. However, we extend mainstream opinions by identifying the potential negative impact of connectedness to nature on human relationships under specific conditions. Specifically, we propose that connectedness to nature promotes dehumanization among anxiously attached people. We tested this assumption with three studies (N = 1276). Studies 1 and 2 revealed that, for people with high levels of anxious attachment, connectedness to nature positively predicted dehumanization of thieves (Study 1) and people who casually litter (Study 2). By manipulating connectedness to nature, Study 3 found that dehumanization elicited by connectedness to nature among people with high attachment anxiety predicted greater preference for nature over prisoners. These trends were eliminated or even reversed for those with low levels of anxious attachment. The present research enriches our understanding of people's social relationships with nature and humans.