Electrochemical intercalation of sodium ions into C60 or C60/C70 mixtures has been obtained in solid state cells working with a ionic conducting polymeric electrolyte. Low speed cyclic voltammetry and low intensity galvanostatic charge experiments give evidence for five successive redox states, as previously noticed for lithium ion intercalation. Reduction potentials of fullerene are strongly dependent on the experimental elaboration conditions of the composite working electrode (fullerene associated with a binding material) and on the open circuit voltage of the cell before intercalation. Preliminary X-ray and electron diffraction studies have allowed the identification of different NaxC60 phases.