An imaging system lens assembly includes five lens elements, the five lens elements 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 and a fifth lens element. Each of the five lens elements has an object-side surface towards the object side and an image-side surface towards the image side. The first lens element has positive refractive power, the object-side surface of the first lens element is convex in a paraxial region thereof.