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This investigation describes the development of AlGaInP light-emitting diodes (LEDs) with a nanometer diameter of porous anodic alumina (PAA) films which are formed by anodization technique to improve and modify the light extraction efficiency. The pore-widening time was changed for surface modulation to obtain the optimum light extraction efficiency. The diameter of nano-pores varies from 30 nm to 60 nm and the interpore spacing is about 75 nm. The light output intensity of the PAA LEDs with 40 minutes pore-widening is 1.39 times that of conventional LEDs. PAA films can effectively reduce critical angle loss, Fresnel loss and be used as scattering center to improve the light extraction.