This invention provides an imaging lens system comprising two non-cemented lens elements with refractive power: a positive first lens element having a convex object-side surface at a paraxial region and a convex or flat image-side surface at the paraxial region; and a negative second lens element having a concave object-side surface at a paraxial region and a concave image-side surface at a paraxial region, and both the object-side and image-side surfaces being aspheric; wherein, the shape of the image-side surface of the second lens element changes from concave when near an optical axis to convex when away from the optical axis. By such arrangement, the imaging lens system has not only a shorter total track length for compact electronic products, but also the advantage of a more comparable focusing performance between the short wavelength and long wavelength applications with improved image quality.