Abstract: An interdental brush includes a handle, a shank extending therefrom, and a bristle portion disposed around the shank. The bristle portion has a plurality of bristle units, each of which has a loading surface facing the handle and having a diameter larger than a diameter of the shank, and a surrounding wall extending from the loading surface toward a direction opposite to the handle with the extent progressively decreasing therefrom. The loading surface and the surrounding wall converge at a brim. The gradually-reduced arrangement of each surrounding wall facilitates an easy entrance into slits between teeth and provides each loading surface and brim with sufficient support to scrape and remove food debris and tartar while pulling the brush out. The revolution of bristle units around the shank helps the brush touch and massage gingivae in a large area, thereby increasing the effect of cleaning teeth and convenience of use.