It is an object to provide a liquid crystal display device capable of displaying a moving image with high image quality by employing a time-division display system (also called a field-sequential system) with the use of a plurality of light-emitting diodes (hereinafter referred to as LEDs) as a backlight. Further, it is an object to provide a liquid crystal display device in which high image quality, full color display, or low power consumption is realized by adjustment of the peak luminance. After a liquid crystal layer is sealed between a pair of substrates, polymer stabilization treatment is performed with the use of UV irradiation from both above and below the pair of substrates at the same time, whereby the polymer included in the liquid crystal layer sandwiched between the pair of substrates is evenly distributed. Thus, a liquid crystal display device is manufactured.