[Issues to be solved] To provide Au alloy wire for ball bonding, which is superior wire strength, and also is superior at formability of molten ball and roundness of compressed ball, moreover is superior at stitch bondability; is available for high density wiring of semiconductor divices. [Solution means] Au alloy wire for ball bonding comprising: 15 - 50 wt ppm Mg, 10 - 30 wt ppm Ca, 5 - 20 wt ppm Eu, 5 - 20 wt ppm Y, 5 - 20 wt ppm La and residual Au is more than 99.998 wt % purity, moreover, purity of more than 99.98 wt % Au, mass of additive Ca is less than the value of total amount of additive Eu and additive La, and mass of additive Y is less than the value of total amount of additive Ca and additive Eu, and mass of 20 - 40 wt ppm Mg.