An image system lens assembly includes, in order from an object side to an image side, a first lens element, a second lens element, a third lens element, a fourth lens element, a fifth lens element and a sixth lens element. The first lens element with negative refractive power has a convex object-side surface and a concave image-side surface. The second lens element has positive refractive power. The third lens element has refractive power. The fourth lens element with negative refractive power has a concave object-side surface and a convex image-side surface. The plastic fifth lens element with positive refractive power has at least one aspheric surface. The plastic sixth lens element with refractive power has a convex object-side surface and a concave image-side surface, and has at least one aspheric surface, wherein the image-side surface thereof changes from concave at a paraxial region to convex at a peripheral region.