The organic nonlinear optical crystal L-threonine was grown from aqueous solution at various pH values and subjected to optical and laser damage characterization. Optical band gap at all pH values has been determined by Uv-Vis-NIR spectra in the range of 190 to 1100 nm using Tauc's method. Measuring transmittance permitted the calculation of extinction coefficient K, refractive index n, and both the real Iecyrillic, ukrainianr and imaginary Iecyrillic, ukrainiani components of the dielectric constant as functions of photon energy. The refractive index of the crystals has been estimated using Abbe's refractometer. The laser damage threshold energy has been measured by irradiating laser beam using a Q-switched Nd: YAG laser (1064nm).L-threonine shows good transmission and high laser damage threshold at isoelectric pH. The results have been discussed in detail.