Q-switched Nd:YAG laser uses two wavelength of 1064nm and 532nm with very short pulse duration time, thus irradiated laser is absorbed in melanin pigment selectively without damaging surrounding tissues. Wavelength of 532nm mainly destroys pigments in epidermis such as freckle, lentigo due to its short penetration, and wavelength of 1064nm treats pigments in dermis such as tattoo, nevus of ota due to its long penetration.