The present invention relates to an optical unit and light guide plate and ink thereof. The ink includes a base resin and a plurality of fine particles. The base resin has a first refractive index. The fine particles have a second refractive index and are dispersed in the base resin. The fine particles are made of organic polymer. The difference between the first refractive index and second refractive index is less than 0.15. The use of the ink will lower the color difference and the variation of color temperature of the light guide plate or the optical unit.