There is provided a hammer shank for a piano which is capable of suppressing a change in the dimension between two arms due to dryness and wetness to thereby ensure smooth and stable operation of a hammer. A hammer shank is supported by a flange and pivotally moves in accordance with key depression. A shank body formed of wood has two bifurcated arms formed on one end thereof. These arms extend in facing and parallel relation to each other along respective opposite sides of the flange, and are pivotally supported by the flange. Phenol backers are attached on outer side surfaces of the respective two arms so as to prevent the two arms from being displaced in a direction in which they face each other.