The present invention relates to a silver alloy bonding wire having silver as the main component. More specifically, provided is a silver alloy bonding wire containing palladium (Pd) of 1-4 wt%, wherein the ratio of a mean grain size (a) of the outer portion to a mean grain size (b) of the center portion with respect to a cross section in the longitudinal direction of the bonding wire is in the range of 0.3-3. When utilizing the bonding wire of the present invention, bonding having excellent high ball formability and SOB bonding property can be obtained inexpensively.