Organic light-emitting diodes (OLEDs) hold great promise as low-cost and large-area electro-optical devices. However, it is important to increase their efficiency for display and lighting applications because of the limited light extraction and absorption in conventional device architectures. In this study, we fabricated a biomimetic transparent brightness enhancement layer (BEL) using cicada wings and applied it to OLEDs. The BEL not only reduced the reflection at the interface between air and glass to 1.4% but also enhanced the transmittance to 91.6%. In addition, the light outcoupling of the OLEDs was increased by approximately 22.2% by employing the biomimetic BEL. The light-emission efficiency of the current OLEDs was improved using the bioinspired structure based on cicada wings.