We present and discuss X-ray absorption spectroscopy and resonant photoemission measurements on Fe nanostructures self-assembledon MgO(001). For Fe coverages below 1 ML equivalent we measured an increase of the Fe L23 branching ratio and changes in thesplitting, widths and relative intensities of the different final states in the L3M23M23 resonant Auger peak. Scanning tunnelling microscopyindicates that the average lateral dimensions of the self-aggregated structures decrease with decreasing Fe amount, from 12 nm at15 ML nominal Fe amount to 5 nm at 2 ML Fe. This observation allows to interpret the observed changes in the 3d band electronicproperties in terms of the evolution of the Fe local atomic coordination from a bulk-like situation to a configuration where low dimensionalityeffects are significant._ 2007 Elsevier B.V. All rights reserved.