Novel inclusion complexes between host microporous molybdenum(II) dicarboxylates (fumarate, terephthalate, trans-trans-muconate, and pyridine-2,5-dicarboxylate) and guest organic polyethers (poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG)) of various molecular weights were synthesized. The rate of complex formation depends on the shapes of the micropores and polyethers. The amount of included polyethers increased with their molecular weight, and reached a saturated amount, with the exception that molybdenum(II) pyridine-2,5-dicarboxylate did not form complexes with bulky PPG. The amount of adsorbed argon in the microporous molybdenum(II) dicarboxylates decreased with increased amounts of included polyethers. The C-13 CP/MAS NMR measurement of molybdenum(II) terephthalate with PEG demonstrated that PEG chains are included in the capillaries. This is an effective method for synthesizing supramolecular complexes.