In this work, the synthesis and molecular adsorption properties of cubic cesium salts of Keggin-type silicododecametalates (SiM; M = W or Mo) and borododecatungstate (BW) blends were reported. Pentavalent BW, which is normally packed in a monoclinic fashion, could be packed into the desired cubic fashion by being blended with tetravalent SiW or SiMo. By simply mixing aqueous solutions containing SiM and BW in different SiM:BW molar ratios [SiM:BW = N:(100 - N), where N is the percentage of SiM in the synthetic solution and equals 100, 80, 50, 30, 20, 10, or 5] with a cesium nitrate solution, we obtained a series of cubic cesium salts (CsSiMBW-N) with POM vacancy-like pores (i.e., kinetically formed interparticle pores). Notably, the yields, compositions, and BET surface areas of the obtained CsSiMBW-N were dependent on only the N values and independent of SiW or SiMo. In CsSiMBW-N, SIM and BW were well blended at the molecular (nanometer) level. The nitrogen, water, and ethanol adsorption properties of CsSiWBW-N systematically changed according to the SiW:BW molar ratios. In the case of SiW-rich salts, nitrogen, water, and ethanol were adsorbed in the pores; the amounts of nitrogen, water, and ethanol adsorbed were nearly identical for CsSiWBW-100. When the SiW:BW molar ratio was decreased, the salts selectively incorporated water and ethanol within the pores. In the case of CsSiWBW-5, barely any nitrogen was adsorbed. The plausible mechanisms for particle growth and interparticle POM vacancy-like pore formation are also discussed.