In recent years rare-earth manganese oxide compounds have been the object of numerous studies because of their large magnetoresistance. The (Nd,Sm)0.5Sr0.5MnO3 compounds have been reported to exhibit magnetic-field-induced first-order phase transitions as well as striction coupled magnetoresistance properties.12 We have prepared samples across the (Nd1-xSmx)0.5Sr0.5MnO3 series with x=0, 0.25, 0.50, 0.75, and 1.0 to study the physical properties of this system. The x-ray diffraction studies revealed that all samples have almost identical patterns with a few very weak additional reflections on the Nd-rich end that are due to the presence of (≪5%) of the SrMnO3 phase. The observed x-ray diffraction patterns matched with the La0.8Sr0.2MnO3-type monoclinic structure (S.G. P2/c) with lattice parameters a=5.429 Å, b=5.450 Å, c=7.652 Å, and B=90.2°. The slight distortion of angle B from 90° suggests that the x-ray data may also be indexed by a closely related GdFeO3-type (S.G. Pbnm) orthorhombic structure reported for a single-crystal sample in Ref. 1. However, our observed intensity pattern matched better with the former structure. A ferromagnetic state was observed below 250 K for x=0 and the mag- netic ordering temperature shifted to lower temperatures with increasing x: the x=1 sample showed magnetic ordering at temperatures below 150 K, in agreement with the published results.2 The samples exhibited a marked field dependence below the ferromagnetic ordering temperature but preliminary data on polycrystalline samples did not show a first-order transition from a metallic ferromagnetic to nonmetallic antiferromagnetic state that has been reported for a single-crystal sample with x=0 (Ref. 1). © 1997 American Institute of Physics.