An optical diffusing film and a LCD backlight using the same are provided. The optical diffusing film comprises a transparent substrate made of an optically transparent material with a refractive index of 1.4 to 1.8, and a diffusing coating with a refractive index of 1.4 to 1.7 disposed on an upper surface of the transparent substrate, wherein diffusing particles with a refractive index of 1.4 to 1.7 are distributed in the diffusing coating, and the diffusing particles are in close contact with each other, the diffusing coating has a thickness of ½ to ⅔ of the largest particle size of the diffusing particles, and the coating density of the diffusing particles is 103 to 106 particles per square millimeter.