A series of pyrochlore oxides, R 2 Ru 2 O 7 (R = Pr 3+ , Sm 3+ -Ho 3+ ) were synthesized under mild hydrothermal conditions. All the samples crystallize in uniform octahedron characteristically. The products were characterized by powder X-ray diffraction, scanning electron microscopy, energy-disperse X-ray spectroscopy, and dc susceptibility, and the factors that affected the crystallization were discussed. It was found that the purity of products depends strongly on the raw materials and the amount of alkalinity in the initial reaction mixtures. The ZFC and FC susceptibilities of all of the compounds R 2 Ru 2 O 7 at low temperature were also measured and discussed.hydrothermal synthesis, pyrochlore compounds, magnetic properties