The substituted samples with nominal compositions of La,Th1-xV2O7-delta (x=0-0.5) were synthesized for the first time by ceramic route and the phase characterization was carried out by powder XRD technique. In addition to substitution at some of the thorium sites in ThV2O7, the substituted samples comprised of two new phases, viz., Th(VO3)(4) and LaTh(VO4)(3-delta). The relative amount of these three constituent phases in a particular sample depended upon the value of x. Furthermore, the DTA/TG results revealed that the presence of La led to suppression of the polymorphic behavior of ThV2O7. The stability of these compounds in hydrogen atmosphere was monitored using temperature programmed reduction (TPR) method. As compared to ThV2O7 and Th(VO3)(4), the LaTh(VO4)(3-delta) phase was found to reduce at higher temperatures. (C) 2004 Elsevier B.V. All rights reserved.