An optical imaging lens system comprising five lens elements (E1, E2, E3, E4, E5), the five lens elements (E1, E2, E3, E4, E5) 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) and a fifth lens element (E5), and each of the five lens elements (E1, E2, E3, E4, E5) 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 of the optical imaging lens system is five, the first lens element (E1) has positive refractive power, the image-side surface of the fourth lens element (E4) is concave in a paraxial region thereof, the object-side surface of the fifth lens element (E5) is convex in a paraxial region thereof, and the image-side surface of the fifth lens element (E5) is concave in a paraxial region thereof; wherein a focal length of the optical imaging lens system is f, a focal length of the second lens element (E2) is f2, a focal length of the fourth lens element (E4) is f4, a focal length of the fifth lens element (E5) is f5, a curvature radius of the object-side surface of the third lens element (E3) is R5, a curvature radius of the image-side surface of the third lens element (E3) is R6, a curvature radius of the image-side surface of the fifth lens element (E5) is R10, an axial distance between the first lens element (E1) and the second lens element (E2) is T12, an axial distance between the second lens element (E2) and the third lens element (E3) is T23, an axial distance between the third lens element (E3) and the fourth lens element (E4) is T34, an axial distance between the fourth lens element (E4) and the fifth lens element (E5) is T45, and the following conditions are satisfied: − 1.85 < f / f 4 < 0.25 ; − 0.20 < f / f 5 < 2.00 ; − 1.30 < R 5 + R 6 / R 5 − R 6 < 2.00 ; 0.30 < f 5 / f 2 < 2.60 ; 0.55 < T 34 / T 12 + T 23 + T 45 < 5.50 ; 0.60 < T 12 / T 45 < 6.00 ; and 0.20 < f / R 10 . wherein a total number of lens elements of the optical imaging lens system is five, the first lens element (E1) has positive refractive power, the image-side surface of the fourth lens element (E4) is concave in a paraxial region thereof, the object-side surface of the fifth lens element (E5) is convex in a paraxial region thereof, and the image-side surface of the fifth lens element (E5) is concave in a paraxial region thereof; wherein a focal length of the optical imaging lens system is f, a focal length of the second lens element (E2) is f2, a focal length of the fourth lens element (E4) is f4, a focal length of the fifth lens element (E5) is f5, a curvature radius of the object-side surface of the third lens element (E3) is R5, a curvature radius of the image-side surface of the third lens element (E3) is R6, a curvature radius of the image-side surface of the fifth lens element (E5) is R10, an axial distance between the first lens element (E1) and the second lens element (E2) is T12, an axial distance between the second lens element (E2) and the third lens element (E3) is T23, an axial distance between the third lens element (E3) and the fourth lens element (E4) is T34, an axial distance between the fourth lens element (E4) and the fifth lens element (E5) is T45, and the following conditions are satisfied: − 1.85 < f / f 4 < 0.25 ; − 0.20 < f / f 5 < 2.00 ; − 1.30 < R 5 + R 6 / R 5 − R 6 < 2.00 ; 0.30 < f 5 / f 2 < 2.60 ; 0.55 < T 34 / T 12 + T 23 + T 45 < 5.50 ; 0.60 < T 12 / T 45 < 6.00 ; and 0.20 < f / R 10 . <EOS>