Ni and Si3N4 layers have been alternatively deposited by sputtering in order to study Ni clusters embedded in amorphous Si3N4. The nominal Ni layer thickness has been varied from 2 to 60 Å and the number of layers was planned to have a similar total amount of Ni. The decrease in the Ni-Ni coordination number observed by Extended X-ray Absorption Fine Structure spectroscopy has been used to study the microstructure of the Ni clustering. For small Ni layer thickness, the actual Ni layer becomes discontinuous and an average cluster diameter of Ni clusters can be determined. Ni metallic cluster in the Ni/Si3N4 system show a magnetization smaller than in bulk nickel, the decrease of magnetization of the cluster should be attributed to a dead skin at the surface of the Ni-clusters.