A new mixed-valence uranium germanate and the silicate analogue have been synthesized under hydrothermal conditions at 600 degrees C and 165 MPa. Their crystal structures contain infinite -U-V-O-U-IV/V-O-U-IV/V-O-U-V- chains that are connected by Ge2O7 or Si2O7 groups to form a 3D framework with six-ring channels where the Cs+ cations are located. Two of the Cs sites in the germanate are partially occupied. Bond-valence-sum calculation and an U 4f X-ray photoelectron spectroscopy study confirm the valence states of the uranium.