The influence of trace addition of Ag on the weldability of an Al-Zn-Mg-Cu-Zr base AA 7010 alloy has been examined. Qualitative Houldcroft test and quantitative varestraint test results showed that Ag addition to the 7010 alloy greatly reduces the hot cracking susceptibility during solidification of welds produced by gas tungsten arc welding process. It is demonstrated that the improvement in the weldability is due to the grain refinement in the weld structure and that this behaviour is comparable to that due to the known influence of Se on the grain refinement and the weldability of the 7010 alloy.