One of the most promising recycling procedures of some industrial organic wastes, as paper mill sludge (PMS), is soil amendment. In this field of application, PMS and natural soil are mixed together according to specific regulations to avoid potential environmental risks that can arise after land restoration, and hence, the mixture must be scrupulously characterized and evaluated, also by means of different analytical techniques. Proton nuclear magnetic resonance (1H NMR) is a powerful, noninvasive and nondestructive technique to investigate natural and artificial porous media, and it is a promising tool to characterize amended soils as well, also in the light of the experimental difficulties that these materials generally entail. In this work, NMR micro- and macro-porosity were related to total organic carbon (TOC) content, and information on the behavior of organic matter (OM) contained inside the mineral matrix was obtained. In particular, a high presence of TOC shows that micropores are forbidden to the saturating water, giving evidence of OM interactions with soil microstructure. This kind of analysis has clear implications in the characterization of amended soil biological processes, such as biodegradation.