In an aim to identify the true active site, we have developed a new probe-assisted NMR technique which allows a genuine differentiation of surface active sites from various facets of a crystallite. Just as XRD giving structure-fingerprint of a crystal bulk, this surface-fingerprint methodology can provide not only qualitative (chemical shift) but also quantitative (peak intensity) surface information for unambiguous activity correlation. Our methodology for facet characterization therefore gives new insights to resolve the current debates and confusions in some facet-dependent properties in literature. Most importantly, our effort to catalysis can largely benefit the fundamental understanding of reaction mechanisms by directly linking well-defined surface structures with their intrinsic reactivity.