Calcium uranium dititanate pyrochlore ( A 2 B 2O 7), a component of a high-level nuclear waste ceramic, was characterized by powder X-ray diffraction, analytical electron microscopy and selected area electron diffraction. The cubic unit cell ( a = 10.1579(5) Å) has symmetry Fd 3m with A in 16( c), B in 16( d), O 1 in 48( f), and O 2 in 8( a). A preliminary examination of the peak intensity in X-ray powder patterns and chemical analyses by energy dispersive X-ray spectroscopy suggest that although this pyrochlore can be approximately described by the crystallochemical formula [Ca, U][Ti 2]O 7 the Ca U ratio may deviate from unity with some trivalent titanium partitioning onto the A-site.