Large single grain high-temperature(Tc) RE-Ba-Cu-O (RE : rare-earth elements) bulk superconductors show the large levitation force and the magnetic flux density. The high-Tc RE-Ba-Cu-O superconductors have great potential for the applications using the superconductor-magnet performance such as the flywheel energy storages systems, the levitation transportation, the superconducting permanent magnets, and so on. To realized the practical applications at the high magnetic fields, the brittleness of the oxide superconductors owing to the complicated crystal structure should be improved. In this study, metallic Ag powder was added to Gd1.5Ba2Cu3O7-y(Gd1.5) bulk superconductors with an aim of improving the mechanical properties of the oxide superconductors. The thermal analysis was carried out for the Gd1.5-Ag systems to understand the formation nature of the GdBa2Cu3O7-y(Gd123). A superconducting critical temperature(Tc), critical current density(Jc), magnetic levitation force(Fm) and magnetic flux density(H) and microstructure of G1.5-Ag bulk superconductors were examined. The optical microscope investigation for the top-seed melt growth(TSMG) processed Gd1.5 with Ag additions showed that Ag particles were observed to fill some of the spherical pores inside the Gd123 grains that formed during melting of Gd123. Additionally, the crack formation induced the phase transformation or thermal shock were greatly reduced by Ag additions. The Tcs of the Gd1.5 with Ag additions were 93 K, which are slightly lower than 93.5 K of the Gd1.5 without Ag addition. The Jcs of the Gd1.5 with 5-20 wt.% Ag additions at 1 Tesla were similar to that of the Gd1.5 with no Ag addition. The Jc of Gd1.5 decreased as the Ag content increased further. The Fms and the Hs of the Gd1.5 with Ag additions also showed a similar tendency to the Tc and Jc. For example, the Fm of the Gd1.5 with 15 wt.% Ag addition was approximately 80% of the Gd1.5 without Ag addition. The property decrease by the Ag addition seems to be attributed to the reduced volume fraction of Gd123 due to the presence of non-superconducting Ag particles inside Gd123 grains and the formation of the subsidiary G123 grains due to the seed(Nd123) melting and recrystallization, which prohibits the growth of the single Gd123 grain. The vickers hardness estimated on the polished surfaces parallel to the a-b plane of Gd123 grains was observed to decrease linearly with as Ag content increased. The fracture toughness values calculated from the hardness data showed that the fracture toughness were increased by the Ag additions. To minimize the property degradation by the Ag addition, the cap-layer process was developed and adapted to the Gd1.5 with Ag additions. The cap pellets with Gd1.5 composition and without Ag addition were placed on the top of Gd1.5-Ag powder compacts and the Gd1.5-Ag compacts with a cap layer were subjected to heating cycles of TSMG process. It was found that Ag particles were presented in the regions of the cap layer. However, the amount of Ag particles in the cap-layer was relatively smaller than that of the Gd1.5 mother compacts. The result indicates that the presence of the cap layer did not prohibits the Ag diffusion from the mother compact completely, but retarded the Ag diffusion to the regions near the Nd123 seed. Consequently, the seed melting was suppressed to some extent. In conclusion, the degradation of the Fm and the H by the Ag addition was minimized by adapting the cap layer process. The magnetic levitation forces at 77 K of the Gd1.5 with a cap layer and 15 wt.% Ag addition was approximately 91-96% of the Gd1.5 with no Ag addition, which is comparable to that of Gd1.5-Ag samples without cap layer.