The metastable pseudomonoclinic perovskite phases, PbY1/23+Nb1/2O3 and PbHo1/2Nb1/2O3 were prepared under conditions of high pressures and temperatures. Investigations of structural parameters, thermal stability and some dielectric properties were carried out. The data were analyzed by comparison with corresponding data of other representatives of the PbB1/23+Nb1/2O3 series. The dependence of unit cell parameters on the B3+ rare earth cation radius for the PbB1/23+Nb1/2O3 perovskites was correlated with a change of electronic structure of the rare earth elements, in particular, with the 4f-shell filling. (C) 2003 Elsevier Science Ltd. All rights reserved.