YBa2Cu3O7 (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 Jc have been studied systematically. Results showed that at fixed physical deposition conditions Jc increased monotonically with number of Ag shots, n, for films grown on both STO and LAO substrates. At 77 K, the Jc increased from 106 to 3.2×106 A/cm2 for LAO and from 8×105 to 3.5×106 A/cm2 for STO as n increased from 0 to 150. At 5 K, the enhancement of Jc was approximately four times at both low and high fields. However, for films grown on YSZ substrate, Jc increased from 2×105 to 2×106 A/cm2 as Ag shots increased from 0 to 30, and decreased to 9×105 for n≥60. Detailed microstructure investigations indicated that the crystallinity and ab alignment gradually improved as the number of Ag-nano-dots increased.