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Cryogenic NMR and NMR spin−lattice relaxation time (NMRT) measurements of pore-confined water (D2O) have been performed using deuterium NMR to probe the pore size distribution (PSD) of silica materials and porous membranes. NMRT measurements were performed at a temperature slightly below the normal freezing point (277 K) of bulk water (D2O) to ensure that all interparticle water was frozen out. PSD derived from cryogenic NMR was in excellent agreement with PSD obtained from N2-adsorption measurements. Also, PSD obtained by NMRT revealed approximately the same average pore dimension as obtained by N2 adsorption. However, the former experimental technique resulted in somewhat narrower PSD than obtained by cryogenic NMR and N2 adsorption and is discussed in the text. An attempt to determine the PSD of a TiO2 membrane on a silica support by NMRT will also be discussed. The main results obtained in this work suggest that a combined use of cryogenic NMR and NMRT may give information on both PSD and pore-connectivity.