© 2019, Pleiades Publishing, Ltd.5-Methyl-4-(3-(2-oxopyrrolidin-1-yl)propyl)-2,4-dihydro-3H-1,2,4-triazol-3-one was synthesized and characterized by X-ray, FTIR and NMR spectroscopic techniques. The molecular geometry and spectral parameters of the title compound were also computed by the DFT/B3LYP76-311++G(d,p) method, and the theoretical data showed a good agreement with the experimental ones. The differences between the theoretical and experimental IR and NMR spectra supported the presence of inter- and intramolecular C-H⋯O and intermolecular N-H⋯O hydrogen bonds, which were revealed by X-ray analysis. Nonlinear optical (NLO) properties of the title compound were analyzed by the DFT/B3LYP/6-311++G(d,p) method by calculating the mean polarizability (α) and first-order hyperpolarizability values (β) (α = 22.0746454×10−24, β = 10.1110649×10−31 esu). As compared with the corresponding data for urea (α = 4.9067×10−24, β = 7.8782×10−31 esu), these values suggest promising NLO properties.