A polymer precursor method has been used to synthesize Ni-doped SnO 2 nanoparticles. X-ray diffraction (XRD) data analyses indicate the exclusive formation of nanosized particles with rutile-type phase (tetragonal SnO2) for Ni contents below 10 mol%. In this concentration range, the particle sizes decrease with increasing Ni content and a bulk solid solution limit was determined at ~ 1 mol%. Ni surface enrichment is present at concentrations higher than the solution limit. Only above 10 mol% Ni, the formation of a second NiO-related phase has been determined. Magnetization measurements suggest the occurrence of ferromagnetism for samples in the solid solution regime (below ~ 1 mol%). This ferromagnetism is associated with the exchange interaction between electron spins trapped on oxygen vacancies, and is enhanced as the amount of Ni2+ substituting at Sn4+ sites increases. Above the solid solution limit, ferromagnetism is destroyed by the Ni surface enrichment and the system behaves as a paramagnet. © 2010 Elsevier B.V. All rights reserved.