A broadband circularly polarized annular ring slot antenna is disclosed, which includes a substrate, an annular ring slot antenna portion located on the upper surface of the substrate, and a microstrip feeding portion located on the lower surface of the substrate. The annular ring slot antenna portion includes a grounding unit, an annular ring slot unit, a central metal unit, a first perturbation metal unit and a second perturbation metal unit. The first perturbation metal unit and the second perturbation metal unit are extended from the grounding unit, towards the central metal unit, respectively. The microstrip feeding portion includes a vertical feeding unit, a bent feeding unit and a rectangular microstrip unit.