A lightweight wheel rim includes a pair of annular side walls, an annular inner wall, and two annular angle elements. The angle elements are disposed respectively at two opposite sides of the inner wall. Each of the angle elements has two opposite sides that are formed respectively and integrally with the inner wall and a radial inner end of a corresponding one of the side walls, and a plurality of alternately arranged mounting portions and dented portions. Each of the mounting portions has a mounting hole for extension of a spoke unit therethrough.