The effects of nanosized silicon oxide nanoparticles and nanowires additions on the microstructure and the normal state transport properties of polycrystalline YBa 2 Cu 3 O y (YBCO, or Y-123) were systematically studied. Samples were synthesized in air using a standard solid state reaction technique by adding nanosized entities up to 3wt.%. Phases, microstructure, superconductivity, have been systematically investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electrical measurements. When nanosized SiO 2 entities are added to the YBCO the orthorhombic structure is maintained. SEM results reveal that the grain size is reduced with increasing the content of SiO 2 . TEM investigation shows the presence of inhomogeneities embedded in the superconducting matrix along with the presence of columnar defects in the case of SiO 2 nanoparticles added samples. Nanowires tend to agglomerate by entangling with each other in the intergrain regions. To analyze the normal state properties of the samples, the percolation theory based on localized states is applied. A change from Coulomb gap to variable-range hopping mechanisms is observed as a result of increasing the nano-entities concentration. The SiO 2 nanowires addition modifies the electrical behavior of samples from metallic to insulating with a much lower concentration comparatively to SiO 2 nanoparticles addition. The localization length d and the range hopping R of samples are estimated.