New complex K~5O~4Na~4H~5[Sn~3(PW~9O~3~4)~2].16H~2O was prepared and its structure was determined by elemental analysis, IR, ^3^1P, ^1^8^3W NMR, polarography, XPS and X-ray crystallography. The anion has A-α-Keggin structure. The new complex crystallize is the monoclinic, P2~1/n with a=1.3625(3)nm, b=2.3625(5)nm, c=2.9306(6)nm, α=90ⅲ, β=99.67(3)ⅲ, γ=90ⅲ, V=9.299nm^3, Z=4.

Key words: SANDWICH COMPOUNDS, HETEROPOLYACID, CRYSTAL STRUCTURE, ELEMENTAL ANALYSIS, INFRARED SPECTROPHOTOMETRY, POLAROGRAPHIC ANALYSIS, PHOSPHORUS 31 MAGNETIC RESONANCE SPECTROMETRY, X-RAY DIFFRACTION ANALYSIS, PHOSPHATE, TUNGSTATE