The trapping of electrons by water clusters and the reaction of positively charged holes in pulsed electron radiolysis of hydrated zeolites X and Y were studied using time-resolved transient absorption spectroscopy. The fully hydrated zeolites, under 12 mbar of water vapor, exhibit a short-lived structureless absorption band centered at 620 nm. This is attributed to hydrated electrons confined to the 13 Angstrom supercages of the zeolites. The band is blue-shifted by 0.28 eV relative to that of the hydrated electrons in bulk liquid water. With the gradual removal of water molecules from the zeolite cavities, a continuous red shift of the transient absorption spectra is observed in both zeolites X and Y. The similarity of the spectral features of hydrated electrons in zeolites to those of water cluster anions in the gas phase suggests that water exists in the form of clusters in the zeolite supercages. The spectral shift with decreasing size of the water clusters presumably demonstrates that the confinement of water by the zeolite cages on the nanometer dimension affects solvation and electronic structures of the excess electrons.