An optical image system includes, in order from an object side to an image side, the first lens element with positive refractive power having a convex object-side surface; the second lens element with refractive power; the third lens element with positive refractive power having at least one surface being aspheric; the fourth lens element with refractive power having a concave object-side surface and a convex image-side surface, wherein at least one surface thereof element is aspheric; the fifth lens element with positive refractive power having a convex image-side surface; and the sixth lens element with negative refractive power made of plastic material and having a concave image-side surface, wherein at least one surface thereof is aspheric, and the image-side surface thereof changes from concave at a paraxial region to convex at a peripheral region.