MicroRNAs (miRNAs) are small RNA molecules that regulate gene expression associated with many complex biological processes. By comparing miRNA expression between long-lived cohorts of Drosophila melanogaster that were fed a low-nutrient diet with normal-lived control animals fed a high-nutrient diet, we identified miR-184, let-7, miR-125, and miR-100 as candidate miRNAs involved in modulating aging. We found that ubiquitous, adult-specific overexpression of these individual miRNAs led to significant changes in fat metabolism and/or lifespan. Most impressively, adult-specific overexpression of let-7 in female nervous tissue increased median fly lifespan by ~22%. We provide evidence that this lifespan extension is not due to alterations in nutrient intake or to decreased insulin signaling.