This invention provides an imaging optical lens assembly including: in order from an object side toward an image side: a first lens with positive refractive power and having a convex object-side surface, a second lens with negative refractive power and having a convex object-side surface and a concave image-side surface, a third lens with positive refractive power and having a concave object-side surface and a convex image-side surface, a fourth lens with negative refractive power and having a concave image-side surface, the object-side and image-side surfaces being aspheric, and a fifth lens having a concave image-side surface, the object-side and image-side surfaces being aspheric. The imaging optical lens assembly further comprises an aperture stop, disposed between an imaged object and the second lens, and an electronic sensor, disposed at the image plane for image formation.