An imaging optical lens system comprising eight lens elements (E1-E8), the eight lens elements (E1-E8) being, 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 and an eighth lens element; wherein a total number of lens elements in the imaging optical lens system is no more than eight, the first lens element with positive refractive power has an object-side surface being convex in a paraxial region thereof, the second lens element with negative refractive power has an object-side surface being convex in a paraxial region thereof and an image-side surface being concave in a paraxial region thereof, the third lens element has positive refractive power, the seventh lens element with positive refractive power has an object-side surface being convex in a paraxial region thereof and an image-side surface being concave in a paraxial region thereof, the object-side surface of the seventh lens element has at least one concave critical point in an off-axis region thereof, the image-side surface of the seventh lens element has at least one convex critical point in an off-axis region thereof, the eighth lens element with negative refractive power has an image-side surface being concave in a paraxial region thereof, and the image-side surface of the eighth lens element has at least one convex critical point in an off-axis region thereof; wherein an Abbe number of the third lens element is V3, an Abbe number of the fifth lens element is V5, an Abbe number of the sixth lens element is V6, a focal length of the seventh lens element is f7, a focal length of the eighth lens element is f8, a curvature radius of an object-side surface of the eighth lens element is R15, a curvature radius of the image-side surface of the eighth lens element is R16, an axial distance between the object-side surface of the first lens element and an image-side surface of the fourth lens element is Dr1r8, an axial distance between an object-side surface of the fifth lens element and the image-side surface of the eighth lens element is Dr9r16, and the following conditions are satisfied: 30 < V6 < 50; 85 < V3 + V5; f 7 / f8 < 25; R16 / R15 < 1.60, and characterized in that the following condition is satisfied: 1.75 < Dr9r 16 / Dr1r8. wherein a total number of lens elements in the imaging optical lens system is no more than eight, the first lens element with positive refractive power has an object-side surface being convex in a paraxial region thereof, the second lens element with negative refractive power has an object-side surface being convex in a paraxial region thereof and an image-side surface being concave in a paraxial region thereof, the third lens element has positive refractive power, the seventh lens element with positive refractive power has an object-side surface being convex in a paraxial region thereof and an image-side surface being concave in a paraxial region thereof, the object-side surface of the seventh lens element has at least one concave critical point in an off-axis region thereof, the image-side surface of the seventh lens element has at least one convex critical point in an off-axis region thereof, the eighth lens element with negative refractive power has an image-side surface being concave in a paraxial region thereof, and the image-side surface of the eighth lens element has at least one convex critical point in an off-axis region thereof; wherein an Abbe number of the third lens element is V3, an Abbe number of the fifth lens element is V5, an Abbe number of the sixth lens element is V6, a focal length of the seventh lens element is f7, a focal length of the eighth lens element is f8, a curvature radius of an object-side surface of the eighth lens element is R15, a curvature radius of the image-side surface of the eighth lens element is R16, an axial distance between the object-side surface of the first lens element and an image-side surface of the fourth lens element is Dr1r8, an axial distance between an object-side surface of the fifth lens element and the image-side surface of the eighth lens element is Dr9r16, and the following conditions are satisfied: 30 < V6 < 50; 85 < V3 + V5; f 7 / f8 < 25; R16 / R15 < 1.60, and characterized in that the following condition is satisfied: 1.75 < Dr9r 16 / Dr1r8.