A single crystal of 5-nitro-2-oxindole was obtained and fully characterized by X-ray structural determination, vibrational frequencies, and UV-vis analysis. An X-ray study indicated that the crystal belongs to a monoclinic crystal system with a P12(1)/n1 space group. Hirshfeld surface analysis was performed for the graphical visualization of the several short intermolecular interactions on the molecular surface. This analysis showed that the major contribution to the crystal structure was the OMIDLINE HORIZONTAL ELLIPSISH (44.9%) interaction. The 2D fingerprint plot supplies the percentage contribution of each atom-to-atom interaction. The non-covalent interaction (NCI) analysis was used to investigate the weak interactions of the atoms in 5-nitro-2-oxindole. The investigation of the influence of the dimeric molecular structure of 5N2Ox on the solubility was carried out in methanol, THF and benzene by using UV-vis spectra. The molecular structure, molecular electrostatic potential (MEP), natural bond orbital (NBO) analysis, and linear and non-linear optical (NLO) properties of 5-nitro-2-oxindole have been investigated using density functional theory (DFT) method at the B3LYP/6-311++G(d,p) level. The electronic properties of the title compound in both the gas phase and in solution (benzene) were examined theoretically using the same method. The vibrational spectra of the dimeric and monomeric forms of 5-nitro-2-oxindole have also been studied using the B3LYP/6-311++G(d,p) method. The assignment of bands in the experimental vibrational spectra of 5N2Ox has been made by comparing its theoretical vibrational frequencies. The scaled frequencies resulted in good agreement with the observed spectral patterns.