The purpose of this work is to study the effect of SiO2- and Al2O3-NPs on the microstructure and mechanical properties of the weld bead (WB) created by a process of Submerged Arc Welding (SAW) between two AISI 1025 steel plates. Also it was necessary consider the chemical compositions of slags and burned fluxes, in order to determine the elements that are deposited and contribute in the final microstructure of WB. The welding materials to form each WB were a M12K electrode, a commercial fused flux (CFF) and AISI 1025 steel plates bevelled at 45°. In addition SiO2- or Al2O3-NPs an ethylic alcohol mixture were applied directly to the beveled surfaces, just before the SAW process, which was carried out according to the AWS A5.17 norm. Microstructural and phase changes at the Heat Affected Zone (HAZ) and Welding Zone (WZ) were analysed by metallographic Optical and Scanning Electron Microscopies. The mechanical properties of the WBs were determined through Tensile, Charpy impact and Vickers Hardness tests. By means of metallography of WBs, it was determined that the length of the AF needles increases in 113 and 183 % when adding SiO2- or Al2O3-NPs, respectively. Related to the mechanical properties of the WB, the tensile and yield strength decreases with both additions, SiO2- or Al2O3-NPs. The microhardness at WZ was found to decrease by adding such oxide-NPs. Moreover, the impact energy absorbed by the WBs increases approximately by 83 or 57% due to SiO2- or Al2O3-NPs addition, respectively.