2-Methylimidazolium hydrogen oxalate dihydrate (2MIO) organic single crystals of good quality have been grown by slow evaporation solution growth technique (SEST). Structure of the compound was determined by single crystal X-ray diffraction (SCXRD) analysis and it reveals that 2MIO crystallized in monoclinic space group P21/n. The high resolution X-ray diffraction (HRXRD) analysis was carried out to find the crystalline quality. The functional groups of 2MIO have been identified by FT-Raman and FT-IR analyses. The optical UV–Vis–NIR transmittance was recorded and the cut-off edge was found at 314 nm. It is worthwhile to mention that the stability and decomposition of the 2MIO material were established by the analysis of TG/DTG and DSC measurements. The crystal hardness was obtained. The dielectric property studies were carried out at different temperatures. Nonlinear optical susceptibility was determined for 2MIO by Z-scan study. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.