The dispersion behavior of Al 2 O 3 and SiO 2 nanoparticles in nickel sulfamate plating baths of different compositions were investigated by Zeta potential measurements and photon correlation spectroscopy ͑PCS͒. The Al 2 O 3 particles have a median diameter of 25 nm and are crystallized in the ␦and ␥-phase. The amorphous SiO 2 particles have a median diameter of 7 nm. In the case of dispersions with Al 2 O 3 particles it was found by PCS that their agglomeration tendency increases with increasing ion concentration of the bath and therefore obeys qualitatively the Delaguin-Landau-Verwey-Overbeek ͑DLVO͒ theory. SiO 2 particles in the same electrolytes show a different behavior: At a specific ion concentration the point of zero charge ͑isoelectric point͒ is shifted to higher pH values. At the highest ion concentration investigated, the particle charge measurements returned zeta potential values of about ϩ15 mV and higher even at pH values up to 6. This result could be explained by an adsorption of Ni 2+ ions on the SiO 2 particle surface. PCS at this dispersion reveals low agglomeration of the SiO 2 nanoparticles in the employed plating bath. The results are discussed.