The effect of Gd 2Ba 6Al 4O 15 powder addition on microstructure, field trapping capability and critical transition temperature, T c, of GdBCOAg superconductors grown in air is reported. Single-grain GdBCO-Ag bulk superconductors with different amounts of Gd 2Ba 6Al 4O 15powder were fabricated by the top seeded melt growth process. Addition of 0.3wt% Gd 2Ba 6Al 4O 15 powder increased the maximum trapped field value, B Zmax. Microstructure analysis confirmed that, up to 1.0wt% addition of this powder, Al-based phase is not formed and Al is supposed to substitute Cu in the GdBa 2Cu 3O 7-δ matrix. Addition of 2.0wt% Gd 2Ba 6Al 4O 15 powder leads to formation of Pt,Al-based phase, which indicates that the solubility limit of Al in the studied system was exceeded. The critical transition temperature, T c, decreases monotonically with increasing Gd 2Ba 6Al 4O 15 powder addition. © 2012 IOP Publishing Ltd.