The　novel　vanadophosphate.　(D　ETA　H)(DETAH(3))(3)[V18O42(PO4)]center　dot(PO4)center　dot　2H(2)O　has　been　synthesized　under　hydrothermal　conditions　and　its　structure　was　determined　by　single-crystal　X-ray　diffraction.　The　compound　crystallizes　in　monoclinic,　space　group　C2/c　with　a　=　23.857(3),　b　=　12.9619(18),　c　20.204(3)　angstrom,　beta　=　105.692(2)degrees,　V　=　6015.0(14)　angstrom(3),　Z　=　4,　D-c　=　2.473　g/cm(3),　M-r　=　2239.68,　F(000)　4432,　R　=　0.0725,　wR　=　0.1524　and　GOOF　=　1.095.　The　metaloxo　cluster　contains　a　novel　six-capped　pesudo-Keggin　structure　unit　which　encloses　a　disorder　PO43-　guest.