Structural properties of NaAlH4/C nanocomposites were studied using 23Na and 27Al solid-state NMR. The samples were synthesized by melt infiltration of a highly porous carbon support, with typical pore sizes of 2−3 nm. Physical mixtures of high surface carbon with alanates in different stages of hydrogen desorption show somewhat broadened resonances and a small negative chemical shift compared to pure alanates. This is most likely caused by a susceptibility effect of the carbon support material, which shields and distorts the applied magnetic field. After melt infiltration, 23Na and 27Al spectra are broadened with a small downfield average shift, which is mainly caused by a chemical shift distribution and is explained by a larger disorder in the nanoconfined materials and a possible charge transfer to the carbon. Our measurements show that the local structure of the nanoconfined alanate is the similar to bulk alanate because a comparable chemical shift and average quadrupolar coupling constant is found. I...