With the aim of producing bulk YBa 2 Cu 3 O y (Y123) superconductors with high flux pinning performance, we employed an infiltration growth (IG) process, in which liquid phase Ba–Cu–O is infiltrated into Y 2 BaCuO 5 (Y211) pellets with NdBa 2 Cu 3 O y seed at high temperatures to produce Y123 phase. Single grain Y123 samples 27mm in diameter and 5mm in thickness could be produced with the seeded IG method. Trapped field measurements showed that the IG-processed Y123 sample was a single domain with the maximum trapped field of around 0.403T at 1mm above the surface at 77K. Magnetization measurements demonstrated that IG-processed Y123 sample exhibits a sharp superconducting transition with an onset T c of around 93.2K. Microstructural observations by means of atomic force microscopy (AFM) clarified that sub-micrometer-sized Y211 particles are finely and uniformly distributed in the Y123 matrix, which is the source of high pinning performances. The critical current density (J c ) values at liquid nitrogen temperature (77K) and 50K in 0T were 1.75×10 5 A/cm 2 and 5.28×10 5 A/cm 2 , respectively. These values are the highest among bulk Y123 samples ever reported in the literature.