YBaCuO (Y123) thin films were grown by pulsed laser deposition (PLD) on YSZ (100), SrTiO3 (100), and LaAlO3 (100) single crystal substrates. Prior to the film deposition, a discontinuous layer of Ag nano-dots was deposited on the substrates. The Y123 films grown on such surfaces modified with Ag nano-dots were characterized by Atomic Force Microscopy (AFM), X-ray diffraction (XRD), scanning electron microscopy (SEM), AC susceptibility and DC magnetization. The effects of the density of Ag nano-dots, which was controlled by the numbers of PLD shots, on the microstructures and resultant critical current density J have been studied systematically. Results showed that at fixed physical deposition conditions J increased monotonically with number of Ag shots, n, for films grown on both STO and LAO substrates. At 77 K, the J increased from 10 to 3.2 × 10 A/cm for LAO and from 8 × 10 to 3.5 × 106 A/cm for STO as n increased from 0 to 150. At 5 K, the enhancement of J was approximately four times at both low and high fields. However, for films grown on YSZ substrate, J increased from 2 × 10 to 2 × 10 A/cm as Ag shots increased from 0 to 30, and decreased to 9 × 10 for n ≥ 60. Detailed microstructure investigations indicated that the crystallinity and ab alignment gradually improved as the number of Ag-nano-dots increased. © 2005 IEEE.