There is provided a subminiature imaging optical system installed in a mobile telecommunication terminal or a PDA, or used in a surveillance camera or a digital camera. The subminiature imaging optical system including: first, second, third and fourth lenses sequentially positioned from an object side to an image side, the first lens having positive refractive power, the second lens having negative refractive power, the third lens having negative refractive power, and the fourth lens having positive refractive power, wherein each of the third and fourth lenses has at least one aspherical surface. The subminiature imaging optical system corrects chromatic aberration superbly to reduce color fringing significantly, thereby achieving high resolution and compactness as well.