A new technique based on nuclear magnetic resonance (NMR) is developed in this paper to determine quantitatively the hydrazide content in poly(oxadiazole-hydrazide) copolymers. Two-dimensional 1H–13C shift correlation and 1H NMR spectra of poly(4,4′-diphenylether-1,3,4-oxadiazole-hydrazide) copolymers with different hydrazide contents were performed to characterize these copolymers and allow for development of a NMR based quantitative correlation for hydrazide content. Thermal gravimetric measurements (TGA) were also performed in order to provide an independent data set for validation of the NMR based technique. The results obtained with the proposed NMR technique were shown to be in good qualitative agreement with the TGA results.