Undoped and amino acid (L-Valine) doped zinc tris (thiourea) sulphate (ZTS) crystals were grown by low temperature slow evaporation solution technique. The cell parameters of grown crystals have been determined by single crystal X-ray diffraction study. The presence of functional groups was studied by FT-IR analysis. The optical transmission analysis shows that the grown crystals have good transparency over the entire visible region from 300 nm. Photoluminescence spectrum of the title materials showed violet emission. The thermal stability of the grown crystals was checked by TG/DTA. The second harmonic generation test for the grown crystals was performed by Kurtz and Perry experimental setup. Third order nonlinear optical (NLO) response of the grown crystals has been examined using a Z-scan technique.