Does the widely documented tendency to prefer natural over built environments owe to the perception of greater restorative potential in natural environments? In the present experimental study we tested the mediating role of restoration in environmental preferences. Participants viewed a frightening movie, and then were shown a video of either a natural or a built environment. We used two examples of each type of environment. Participants’ mood ratings were assessed before and after they viewed the frightening movie, and again after viewing the environmental video. Participants also rated the beauty of the environment shown (to indicate preference) and performed a test of concentration after viewing the environmental video. The results indicate that participants perceived the natural environments as more beautiful than the built environments. In addition, viewing natural environments elicited greater improvement in mood and marginally better concentration than viewing built environments. Mediational analyses revealed that affective restoration accounted for a substantial proportion of the preference for the natural over the built environments. Together, these results help substantiate the adaptive function of people's environmental preferences.