A series of Sr(2)LnTaO(6) (Ln = lanthanides except for La, Ce, and Pr) has been prepared by a standard ceramic method and their crystal structure has been determined by powder X-ray diffraction using the Rietveld analysis method. The crystal symmetry of their oxides is monoclinic (space group P2(1)/n) with an ordered arrangement of Ln and Ta ions. Magnetic susceptibility measurements show that these compounds are paramagnetic down to 5 K. The Eu-151 Mossbauer spectrum for Sr2EuTaO6 indicates that the Eu ion is in the trivalent state. The symmetry of the Eu site is distorted from the octahedral symmetry, and its spin-orbit coupling constant is determined to be 342 cm(-1). In the Yb compound, the energy levels in the octahedral crystal field splitting are determined to be EGamma7-Gamma6 = 1324 and EGamma8-Gamma6 = 391 cm(-1) by calculating the magnetic susceptibility. (C) 2002 Elsevier Science Ltd. All rights reserved.