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, a second lens element, a third lens element, a fourth lens element and a fifth lens element, 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 has positive refractive power, the image-side surface of the fourth lens element is concave in a paraxial region thereof, the object-side surface of the fifth lens element is convex in a paraxial region thereof, and the image-side surface of the fifth lens element 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 is f2, a focal length of the fourth lens element is f4, a focal length of the fifth lens element is f5, a curvature radius of the object-side surface of the third lens element is R5, a curvature radius of the image-side surface of the third lens element is R6, a curvature radius of the image-side surface of the fifth lens element is R10, an axial distance between the first lens element and the second lens element is T12, an axial distance between the second lens element and the third lens element is T23, an axial distance between the third lens element and the fourth lens element is T34, an axial distance between the fourth lens element and the fifth lens element 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 has positive refractive power, the image-side surface of the fourth lens element is concave in a paraxial region thereof, the object-side surface of the fifth lens element is convex in a paraxial region thereof, and the image-side surface of the fifth lens element 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 is f2, a focal length of the fourth lens element is f4, a focal length of the fifth lens element is f5, a curvature radius of the object-side surface of the third lens element is R5, a curvature radius of the image-side surface of the third lens element is R6, a curvature radius of the image-side surface of the fifth lens element is R10, an axial distance between the first lens element and the second lens element is T12, an axial distance between the second lens element and the third lens element is T23, an axial distance between the third lens element and the fourth lens element is T34, an axial distance between the fourth lens element and the fifth lens element 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.