We investigated the effect of Ag addition on cold-seeded melt-growth of Gd-Ba-Cu-O superconductors using Nd123 seed crystal. We found that a small addition of Ag enlarged the temperature window for stable single-grain growth, since the decomposition temperature of Gd123 decreased with Ag addition. However, Ag addition of more than 5 wt.% restricted the temperature window due to the melting of Nd123 seed crystal which reacted with Ag. The employment of a double layered precursor, which composed of two layers with and without Ag, solved the problem of the diffusion of Ag into the seed crystal. As a result, single grain Gd-Ba-Cu-O/Ag bulks could be obtained in a wide temperature window.