We demonstrate a GaN-based high-Q microcavity light emitting diode (MCLED) with a buried AlN current aperture. A thin AlN layer is inserted on the InGaN/GaN multiple quantum wells as a current blocking layer and an optical confinement layer. The GaN-based MCLED is composed of a 29-pair GaN/AlN distributed Bragg reflector (DBR), an eight-pair of SiO2/Ta2O5 dielectric DBR, and a three-λ optical thickness InGaN/GaN active region. The current can be injected more effectively in the MCLED with a buried AlN current aperture. The output emission has a dominant emission peak wavelength at 440 nm with a very narrow linewidth of 0.52 nm, corresponding to a cavity Q-value of 846 at a driving current of 5 mA.