The present disclosure discloses a diaphragm for radiating sound, including: a dome; a suspension surrounding the dome, including a first connecting portion adjacent to the dome and having a first surface and a second surface, a suspending portion extending from and surrounding the first connecting portion, and a second connecting portion extending from and surrounding the suspending portion. The suspending portion includes a convex part along a direction from the second surface to the first surface, an inner edge connecting to the first connecting portion, and an outer edge connecting to the second connecting portion. The diaphragm further includes a stiffening layer located on the first surface of the first connecting portion, extending from the inner edge toward the dome. The present disclosure further includes a speaker incorporating the diaphragm.