Efficiency is a core technical indicator for gallium nitride (GaN)-based light-emitting diodes (LEDs), directly reflecting the performance of the device and providing a reference for subsequent process optimization. Consequently, the accurate and reliable characterization of efficiency is crucial. This chapter begins with an overview of the efficiency of GaN-based LEDs, introducing the definitions of various efficiencies and commonly employed characterization methods. It demonstrates the utility of efficiency characterization in analyzing LED performance and carrier dynamics, supported by typical experimental results. Finally, the chapter discusses the applicability and limitations of the different characterization methods and offers insights into the future development direction of efficiency characterization.