In this paper, we propose the idea that simultaneous analysis of NMR relaxation data and residual dipolar couplings (RDCs) can provide information about interdomain dynamics in a multidomain protein, which cannot be derived from each data set separately. Specifically, such an approach can be useful when the interdomain motions occur on a timescale comparable to or slower than the overall tumbling in solution. We analyze residual dipolar couplings together with 15N relaxation data for Lys48-linked di-ubiquitin (Ub2), in which interdomain dynamics are described as interconversion between two distinct conformational states of the protein. Our results show that 15N relaxation and residual dipolar coupling data can be used as two complementary experimental data sets for consistent characterization of interdomain conformations and dynamics in this dual-domain protein.