A semi organic L–Threonine Ammonium Acetate (L-HAA) crystal has been grown at room temperature by using slow evaporation technique. Single crystal X-ray diffraction analysis reveals that the grown crystal crystallizes in the non-centro symmetric space group C2 of tetragonal crystal system. Infrared spectral analysis has been done to confirm the presence of functional groups in the grown crystal. Thermo gravimetric analysis reveals that the grown crystal is thermally stable upto 201ºC. The second harmonic generation output intensity was confirmed using the Kurtz and Perry powder method and it is found to be 0.986 times lesser than that of KDP.