We have synthesized the cyclic Ti-9 Keggin trimers [(alpha-Ti3PW9O38)(3)(PO4)](18-) (1) and [(alpha-Ti3SiW9O37OH)(3)(TiO3(OH2)(3))](17-) (2), which are both composed of three (Ti3XW9O37) units (X = P or Si) linked via three Ti-O-Ti bridges and a capping group, which is either tetrahedral PO4 (1) or octahedral TiO6 (2). Polyanions 1 and 2 were fully characterized in the solid state (IR, X-ray diffraction, thermogravimetric and elemental analyses) and in solution (P-31 or W-183 NMR).