Functionalized AOT reverse micelles (Ni(AOT)(2)/Na(AOT)) were used in an attempt to form nickel metal nanoparticles. After reduction by sodium borohydride either under nitrogen or in open air, nanoparticles are obtained. However, it is shown by X-ray photoelectron spectroscopy analysis that Ni2B is obtained under nitrogen and a mixture of nickel metal and Ni-B is obtained in open air. The magnetic properties of the samples made in open air or under nitrogen drastically differ and confirm the XPS studies.