Ammonium Dihydrogen Phosphate (ADP) is a pioneer Nonlinear Optical (NLO) crystal. It is widely used in a Laser Technology and Optoelectronics. The pure and various amino acids like L-threonine, L-serine and L-phenylalanine doped ADP crystals are grown using the slow solvent evaporation technique at room temperature. The powder XRD study shows the single phasic body centred tetragonal structure of all the grown crystals. The FT-IR spectroscopy confirmed presence and alteration of various function groups of ADP crystal on doping the amino acids in it. The FT-Raman spectroscopy revelled presence of various normal modes of vibrations for pure and amino acids doped ADP crystals. The Photoluminescence study has shown existence of the Self Trapped Excitons (STE), increase of the stoke shift and the vibration relaxation states. The CHN analysis shows the increase of carbon, hydrogen and nitrogen percentage on increasing the doping concentration of various amino acids in ADP crystal. The TGA/DTA study indicated that the amino acids makes ADP crystal thermally less stable.