The cross-linking process of natural rubber (NR) is studied for the first time by a unique combination of rheology and time-domain (TD) NMR, two methods that are commonly conducted separately. The combined setup consists of a high-end rheometer and a compact 25 MHz 1H NMR relaxometer (rheo-NMR), which allows rheological characterization and NMR relaxometry to be operated simultaneously on the same sample. During vulcanization, the elastic modulus G′(t), representing the macroscopic elasticity, was directly correlated to the molecular dynamic parameters derived from NMR, including the population-averaged transverse relaxation rate, 1/T2ave, and the logarithmic mean of the residual dipolar coupling constant, D̅res. It is found that, at the same level of macroscopic elasticity, the conformational flexibility of network chains in NR cross-linked with the so-called efficient vulcanization (EV) is more restricted than that with conventional vulcanization (CV). This can be attributed to the shorter and consequently less flexible (monosulfidic) cross-links formed by EV, whereas polysulfidic links dominate in the CV vulcanizate as confirmed by high-field 13C NMR spectroscopy.