Non linear optical single crystals of L-alanine have been grown from aqueous solution of potassium di hydrogen phosphate (KDP) by the slow evaporation method. Single crystal X-ray diffraction confirms the orthorhombic structure of the grown crystals. Fourier transform infrared (FT-IR) studies reveal the presence of functional groups present in the grown crystal. The optical transmission study reveals very good transparency of the crystal and its optical band gap is found to be 4.9 eV. The thermal stability of the grown crystal is found to be 288.7 °C. The second harmonic generation (SHG) of the material was investigated using pulsed Nd: YAG laser. Third order non linear studies were performed using the single beam Z-scan technique using continuous wave Nd: YAG laser. Closed aperture Z-scan studies reveal negative nonlinearity in the crystals and open aperture Z-scan reveals saturation absorption. Also nonlinear parameter values such as nonlinear refractive index n2, absorption coefficient β and nonlinear optical susceptibility χ(3) were evaluated for the L-alanine crystal. © 2013