An interdental brush includes a handle, a neck, a head and a mounting sleeve. The handle has an upper end provided with a positioning portion. The neck extends from an upper end of the positioning portion. The neck has a helical annular groove which makes the neck flexible and bendable so that the neck can be bent. The helical annular groove contains oblique veins so that the neck is kept at a determined bending angle. The mounting sleeve is mounted on a bottom end of the handle to lengthen the handle. Thus, the neck is bent freely and kept at a determined bending angle by provision of the helical annular groove so that the angle of the head can be adjusted arbitrarily.
