The crystal structures of Ag2Mo2O7(I) and Ag2W2O7(II) have been determined by single-crystal X-ray analysis. Both compounds crystallize in space group P, Z= 2, with for (I): a= 6.095(3), b= 7.501(3), c= 7.681(3)Å, α= 110.4(1), β= 93.3(1), γ= 113.5(1)°; and for (II): a = 6.033(3), b= 7.051 (3), c= 7.735(3)Å, α= 73.8(1), β= 92.2(1), γ= 104.7(1)°. The structures were determined from diffractometer data by heavy-atom methods and refined to R 0.045 [(I), 1 208 observed reflections] and 0.047 [(II), 1 364 observed reflections]. The structures consist of infinite chains formed by blocks of four edge-shared octahedra joined by edge-sharing in (I), and by corner-sharing in (II), with the silver ions situated between the chains.