This invention relates to a backlight unit of a liquid crystal display device using a cold cathode fluorescent lamp that is capable of realizing pure colors and having a broad color reproduction range. A backlight unit of a liquid crystal display device according to an embodiment of the present invention includes at least one lamp including a first red phosphor having a dominant wavelength of about 620 nm, a second red phosphor having a dominant wavelength of about 658 nm, a green phosphor having a dominant wavelength of about 515 nm and a blue phosphor having a dominant wavelength of about 447 nm; a bottom cover in which the lamp is disposed; and an optical member disposed on the lamp.