The crystal structures of MAs(2)O(6) (M = Pb, Ca) have been redetermined using X-ray powder diffraction data by the Rietveld method. These compounds are trigonal (space group P $($) over bar$$ 31m) with a = 4.875(1) Angstrom and c = 5.504(1) Angstrom for M = Pb, and a = 4.826(1) Angstrom and c = 5.082(1) Angstrom for M = Ca. The agreement factors were R(WP) = 11.8% and R(F) = 3.5% for M = Pb and R(WP) = 10.3% and R(F) = 1.4% for M = Ca. The diffraction peaks show a very strong broadening anisotropic peak shape that has been fitted and results in a remarkable improvement of the description of the structures : This series of compounds has arsenic atoms in a pseudooctahedral environment of oxygens. AsO6 groups are very poorly spectroscopically characterized; hence, we also report the IR and Raman data. The results of the vibrational study are in agreement with the crystal structure, and an initial assignment of the spectra is proposed. We observe a displacement of the intense bands for the AsO4 groups at approximate to 880 cm(-1) (IR active) and approximate to 840 cm(-1) (Raman active) to approximate to 740 and approximate to 750 cm(-1), respectively, for the AsO6 groups.