The crystal structure of $(C_{12}H_{24}O_6{cdot}K)_2K[Co(OH)_6Mo_6O_{18}]{cdot}12H_2O$ has been determined by X-ray diffraction. Crystal data as follows ; monoclinic, space group $C_2/m,;a;=;22.512(4);{AA},;b;=;18.304(4);{AA},;c;=;7.641(1);{AA},;{eta};=;90.52(2);{AA}$, and Z = 2. A final conventional R value of 0.044 was obtained by least-squares refinement of 4173 independent observed $[{mid}Fo{mid}{geq}3{sigma}({mid}Fo{mid})]$ reflections. The $[Co(OH)_6Mo_6O_}{18}]^{-3}$ polyanion shows the well-known Anderson-structure and has approximate 3m symmetry. A $[Co(OH)_6Mo_6O_{18}]^{-3}$ polyanion is located between two crown ether complexed cations forming a sandwich structure. One potassium ion interacts with the crown ether via electrostatic interactions. The other potassium ion only interacts with the water molecules and terminal oxygen atoms of the polyanion.