An imaging optical lens assembly includes nine lens elements which are, in order from an object side to an image side along an optical path: a first lens element, a second lens element, a third lens element, a fourth lens element, a fifth lens element, a sixth lens element, a seventh lens element, an eighth lens element and a ninth lens element. Each of the nine lens elements has an object-side surface facing toward the object side and an image-side surface facing toward the image side. The first lens element has positive refractive power. The second lens element has negative refractive power. The image-side surface of the ninth lens element is concave in a paraxial region thereof and has at least one inflection point.