Organic light-emitting diodes (OLEDs) with two-dimensional photonic crystal were fabricated to improve their light-extraction efficiency. The electroluminescence (EL) spectra from these OLEDs depended on the lattice constant of the photonic crystal. The relationship between the EL spectra and the lattice constant was investigated. On the basis of this investigation, a lattice constant was optimized to obtain a large improvement in luminance. In addition, OLEDs doped with coumarin 6 provided a larger improvement in luminance than nondoped OLEDs. The coumarin 6 doped OLED with the optimized lattice constant provided improvements of 62% in luminance in the normal direction and 25% in spatially integrated EL intensity.