An imaging system lens assembly comprising six lens elements (E1, E2, E3, E4, E5 and E6), the six lens elements (E1, E2, E3, E4, E5 and E6) being, in order from an object side to an image side along an optical path, a first lens element (E1), a second lens element (E2), a third lens element (E3), a fourth lens element (E4), a fifth lens element (E5) and a sixth lens element (E6), and each of the six lens elements (E1, E2, E3, E4, E5 and E6) having an object-side surface facing toward the object side and an image-side surface facing toward the image side; wherein a total number of lens elements in the imaging system lens assembly is six, the first lens element (E1) has positive refractive power, the object-side surface of the fifth lens element (E5) is concave in a paraxial region thereof, the image-side surface of the fifth lens element (E5) is convex in a paraxial region thereof, the image-side surface of the sixth lens element (E6) is concave in a paraxial region thereof, and the image-side surface of the sixth lens element (E6) has at least one inflection point (P); wherein an axial distance between the image-side surface of the sixth lens element (E6) and an image surface (IMG) is BL, an axial distance between the object-side surface of the first lens element (E1) and the image-side surface of the sixth lens element (E6) is TD, an f-number of the imaging system lens assembly is Fno, a curvature radius of the image-side surface of the fifth lens element (E5) is R10, a curvature radius of the object-side surface of the sixth lens element (E6) is R11, a curvature radius of the image-side surface of the sixth lens element (E6) is R12, a focal length of the imaging system lens assembly is f, a focal length of the first lens element (E1) is f1, a focal length of the second lens element (E2) is f2, a focal length of the third lens element (E3) is f3, a focal length of the fourth lens element (E4) is f4, and the following conditions are satisfied: 0.65 < BL / TD < 1.00 ; 1.35 < Fno < 2.30 ; − 65.00 < R 11 + R 12 / R 11 − R 12 < 1.80 ; − 0.90 < f 1 / f 3 < 2.00 ; − 12.00 < f / R 10 < − 1.10 ; and 0.05 < f 2 / f 4 < 0.95 . wherein a total number of lens elements in the imaging system lens assembly is six, the first lens element (E1) has positive refractive power, the object-side surface of the fifth lens element (E5) is concave in a paraxial region thereof, the image-side surface of the fifth lens element (E5) is convex in a paraxial region thereof, the image-side surface of the sixth lens element (E6) is concave in a paraxial region thereof, and the image-side surface of the sixth lens element (E6) has at least one inflection point (P); wherein an axial distance between the image-side surface of the sixth lens element (E6) and an image surface (IMG) is BL, an axial distance between the object-side surface of the first lens element (E1) and the image-side surface of the sixth lens element (E6) is TD, an f-number of the imaging system lens assembly is Fno, a curvature radius of the image-side surface of the fifth lens element (E5) is R10, a curvature radius of the object-side surface of the sixth lens element (E6) is R11, a curvature radius of the image-side surface of the sixth lens element (E6) is R12, a focal length of the imaging system lens assembly is f, a focal length of the first lens element (E1) is f1, a focal length of the second lens element (E2) is f2, a focal length of the third lens element (E3) is f3, a focal length of the fourth lens element (E4) is f4, and the following conditions are satisfied: 0.65 < BL / TD < 1.00 ; 1.35 < Fno < 2.30 ; − 65.00 < R 11 + R 12 / R 11 − R 12 < 1.80 ; − 0.90 < f 1 / f 3 < 2.00 ; − 12.00 < f / R 10 < − 1.10 ; and 0.05 < f 2 / f 4 < 0.95 . <EOS>