A bat for an upright piano is provided for ensuring stable swinging movements of a hammer to generate a proper piano sound even if a hammer assembly has the centroid which is laterally asymmetric about a center pin. The bat for an upright piano is supported by the center pin having a circular cross section and arranged horizontally in a bat flange, in order to swing a hammer to cause the same to strike a string. The bat comprises a bat body integrally formed with the hammer, and having a linear pin holding groove in a back surface thereof, and a metal plate having a linear pin retaining groove in one side thereof, and attached to a back surface of the bat body such that the pin retaining groove extends in parallel with the pin holding groove, wherein the bat is pivotally supported by the center pin while the center pin is in engagement with the pin holding groove and the pin retaining groove, and the center pin is sandwiched between the bat body and the metal plate.