Organic nonlinear optical o-Phenylenediaminium p-Toluene sulfonate single crystal was grown by slow evaporation solution growth method. The crystal system and lattice parameters were confirmed by single crystal X-ray diffraction studies. Thermal stability (246 °C) of the system was observed by thermal studies. UV-Vis spectral studies revealed the lower cut-off wavelength transparency and corresponding band gap. Photoluminescence emission peak of the crystal occurred in yellow region. Third order nonlinear optical properties were elucidated by Z-scan technique and found that the crystal possesses saturable absorption and the self-defocusing effect. © 2019 Elsevier B.V.