There is provided a polarizer for organic light emitting diodes (OLED) having improved brightness. The polarizer, which comprises a linear polarizer and a ¼ retardation plate, comprises a reflective polarizer film disposed between the linear polarizer and the ¼ retardation plate and transmitting a polarized light horizontal to the transmission axis of the linear polarizer while reflecting a polarized light vertical to the transmission axis of the linear polarizer. The polarizer may be useful to highly improve the brightness of the OLED device when the polarizer is used in the OLED device.