Materialism is the focus of much research due to its negative consequences for individuals and societies. While recent research indicates that the strength of materialistic value orientations changes with age during adulthood, little is known about the processes that cause these age-related changes. We propose that changes in materialism, as people grow older, are rooted in changes in self-uncertainty. We find evidence for this idea in two studies and across different measures of self-uncertainty. In addition, we show that the changes in materialism cannot be explained by (age-related) differences in socio-demographic variables. Finally, our results indicate that changes in self-uncertainty provide a better account for changes in materialism than age-related changes in self-esteem.