Building on previous research in existential psychology, we tested whether inducing death anxiety and death reflection differentially inhibit or inspire proenvironmental outcomes, respectively (Hypothesis 1). The outcomes we examined were of biospheric concern, intention to engage in environmental activism, support for population growth mitigation policies, and support for reducing carbon dioxide emissions. We also hypothesized that these differential effects would be more evident for those with less versus more environmentalist contingent self-worth (Hypothesis 2). In an experimental online study (N = 280), neither death anxiety nor death reflection affected proenvironmental outcomes. We only found a marginally significant positive effect of death reflection vs. the control condition on biospheric concern and a marginally significant interaction suggesting death reflection might increase biospheric concern compared to death anxiety among those weak in environmentalist contingent self-worth. Overall, the notion that mortality reminders affect proenvironmental outcomes was unsupported.What is the significance of this article for the general public?Despite plausibility based on extant theory in existential psychology and prior findings on the effect of mortality reminders on proenvironmental outcomes, we did not find evidence that experiences of death anxiety or death reflection have a meaningful impact on proenvironmental outcomes. Although we detected the possibility of a small positive effect of death reflection on biospheric concern, especially for those with less environmentalist contingent self-worth, mortality reminders did not affect activism intention, support for population growth mitigation policies, or support for reducing carbon dioxide emissions.