Two samples of Au 55 (PPh 3 ) 12 Cl 6 organometallic clusters prepared by different methods were investigatcd by X-ray powder diffraction (XRD). The measured diffraction curves were fitted by a set of Debye functions for Au N with the «magic» numbers N=13, 55, 147,... for cuboctahedra and icosahedra; N=54, 181 for decahedra; and N=13, 57, 154 for hexagonal close-packed clusters. It was clearly shown that most Au 55 (PPh 3 ) 12 Cl 6 clusters do not have an fcc structure, but a good fit was achieved using the icosahedral model. The nearest-neighbor distance is 0.278 nm, i.e. ∼3% smaller than that of the bulk gold material (0.288 nm); however, the center of the first coordination shell is uncontracted within the limits of error (0.5%)