Nanobodies are single chain antibodies that have become a highly valuable and versatile tool for biomolecular and therapeutic research. One application field is the stabilization of active states of flexible proteins, among which G-protein coupled receptors (GPCRs) represent a very important class of membrane proteins. Here we present the backbone and side-chain assignment of the 1H, 13C and 15N resonances of Nb33 and Nb39, two nanobodies that recognize and stabilize the μ-opioid receptor (μOR) to opioids in its active agonist-bound conformation. In addition, we present a comparison of their secondary structures as derived from NMR chemical shifts.