Quantitative X-ray powder Rietveld refinements for a series of alloys from the solid solution EuyFe4−xNixSb12, synthesized by argon arc-melting followed by long term annealing, established in all cases isotypism with the partially filled skutterudite-type structure, LaFe4P12. The Eucontent of the samples was determined from the combined data obtained results of Rietveld refinements and electron microprobe measurements. These investigations confirmed a systematic trend for the Eu-occupancy y in the parent lattice, revealing a gradual decrease of the maximum Eu-content from practically full occupancy, y = 0.83, in Eu0.83Fe4Sb12 to y ∼ 0.5 for Eu∼0.5Fe2Ni2Sb12. Eu0.83Fe4Sb12 orders magnetically below 84 K and the transition temperature decreases as a function of Fe/Ni substitution. As a further consequence of the Fe/Ni substitution electronic transport crosses over from a hole conductivity regime into electron dominated behaviour. Concomitantly, the transition metal exchange increases the Seebeck coefficient significantly, hence the figure of merit enhances.