RbC24 and CsC24 were allowed to react with isoprene, styrene or 1,3-butadiene. RbC24 expanded slowly along the c-axis direction through contact with these unsaturated hydrocarbons. Monomer molecules are considered to be introduced into the interlayer of RbC24 and polymerized. In the case of CsC24, isoprene was polymerized in a similar manner as RbC24 and KC24, whereas the reactivity of styrene and I,3-butadiene was low. The different reactivities are explained on the basis of the activity of polymerization initiators. The reactivity of monomers to polymerize in a certain GIC is in the following order: isoprene > 1,3-butadiene > styrene, which is the reverse order of reactivity recognized in the conventional polymerization.