This paper presents a study of the synthesis and structural properties of the new pyrochlore-type Bi 2 À y Sr y Ir 2 O 7 series. Ten compositions with 0.0 r yr 0.9 were prepared by solid-state reaction with thermal treatments at 873, 1073 and 1323 K under atmospheric pressure conditions. Structural refinements from X-ray powder diffraction data by the Rietveld method show that all compounds of the Bi 2 À y Sr y Ir 2 O 7 solid solution crystallize in a a-pyrochlore structure. The main structural difference when bismuth is substituted by strontium concerns the x position of the O1 (x, 1 / 8 , 1 / 8 ). This substitution significantly increases the Bi/Sr-O1 distance and diminishes the Ir-O1 distance; this implies that the Ir-O1-Ir bond angle increases. With the Sr substitution, the IrO 6 local configuration goes from a flattened trigonal antiprism, yo 0.5, to an elongated one, y4 0.5, passing through an octahedral array, y $ 0.5. The electrical consequences of these structural changes observed in this system are qualitatively explained with electronic structure calculations, this behavior agrees very well with those observed in other pyrochlore systems A 2 M 2 O 7 (A¼ rare earth cations or Tl þ , Pb 2 þ , or Bi 3 þ , and M¼ Ru or Ir).