This paper presents how various additions of Al2O3 nanoparticles in the electrolytic bath modified the Ni/Al2O3 nanocomposite coating microstructure. The residual stresses, lattice defects, and crystallographic texture of the obtained deposits were studied. The investigations showed that the tensile residual stresses corresponded to the ceramic nanoparticles content in the deposited coating. The high level of measured stresses in the Ni/Al2O3 coatings indicated the presence of strengthening mechanisms caused by the Al2O3 nanoparticles. The density of crystal lattice defects and grain refinement contributed to the strengthening of the Ni matrix. The main texture components and lattice parameters were more sensitive to deposit thickness changes than to the amount of alumina nanoparticles embedded in the coatings. The Ni/Al2O3 with the smallest thickness showed the highest lattice parameters of the Ni matrix.