A crystal of dimensions 2.5 × 2.5 × 1.8 mm and of composition Mo3.25Ir was examined by neutron diffraction at 293 and 10 K. It has the A15 structure for which the space group isPm3nand the ideal composition would be Mo3Ir. Least‐squares refinements gaveR(F) values of 0.013 and 0.017 for the 293 and the 10 K data, respectively. No structural phase transition was observed at 10 K. The lattice constants found werea= 4.967 (2) Å at 293 K and 4.958 (2) Å at 10 K. The transition temperature to superconductivity of the crystal was measured by an inductive method. An onset of superconductivity was found at 9.25 (5) K and a main transition at 9.10 (5) K. Another, approximately cylindrical, sample of volume 117 mm3showed an onset at 8.6 (1) K and a main transition at 8.0 (1) K. About two